Chapter 17. Stored Procedures and Functions
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## Chapter 17. Stored Procedures and Functions

Stored routines (procedures and functions) are supported in MySQL 5.0. A stored procedure is a set of SQL statements that can be stored in the server. Once this has been done, clients don't need to keep reissuing the individual statements but can refer to the stored procedure instead.

Some situations where stored routines can be particularly useful:

- When multiple client applications are written in different languages or work on different platforms, but need to perform the same database operations.

- When security is paramount. Banks, for example, use stored procedures and functions for all common operations. This provides a consistent and secure environment, and routines can ensure that each operation is properly logged. In such a setup, applications and users would have no access to the database tables directly, but can only execute specific stored routines.

Stored routines can provide improved performance because less information needs to be sent between the server and the client. The tradeoff is that this does increase the load on the database server because more of the work is done on the server side and less is done on the client (application) side. Consider this if many client machines (such as Web servers) are serviced by only one or a few database servers.

Stored routines also allow you to have libraries of functions in the database server. This is a feature shared by modern application languages that allow such design internally (for example, by using classes). Using these client application language features is beneficial for the programmer even outside the scope of database use.

MySQL follows the SQL:2003 syntax for stored routines, which is also used by IBM's DB2.

The MySQL implementation of stored routines is still in progress. All syntax described in this chapter is supported and any limitations and extensions are documented where appropriate. Further discussion of restrictions on use of stored routines is given in Section I.1, “Restrictions on Stored Routines and Triggers”.

Binary logging for stored routines takes place as described in Section 17.4, “Binary Logging of Stored Routines and Triggers”.

## 17.1. Stored Routines and the Grant Tables

Stored routines require the `proc` table in the `mysql` database. This table is created during the MySQL 5.0 installation procedure. If you are upgrading to MySQL 5.0 from an earlier version, be sure to update your grant tables to make sure that the `proc` table exists. See Section 5.6.2, “mysql_upgrade — Check Tables for MySQL Upgrade”.

The server manipulates the `mysql.proc` table in response to statements that create, alter, or drop stored routines. It is not supported that the server will notice manual manipulation of this table.

Beginning with MySQL 5.0.3, the grant system takes stored routines into account as follows:

- The `CREATE ROUTINE` privilege is needed to create stored routines.

- The `ALTER ROUTINE` privilege is needed to alter or drop stored routines. This privilege is granted automatically to the creator of a routine.

- The `EXECUTE` privilege is required to execute stored routines. However, this privilege is granted automatically to the creator of a routine. Also, the default `SQL SECURITY` characteristic for a routine is `DEFINER`, which enables users who have access to the database with which the routine is associated to execute the routine.

## 17.2. Stored Routine Syntax

A stored routine is either a procedure or a function. Stored routines are created with `CREATE PROCEDURE` and `CREATE FUNCTION` statements. A procedure is invoked using a `CALL` statement, and can only pass back values using output variables. A function can be called from inside a statement just like any other function (that is, by invoking the function's name), and can return a scalar value. Stored routines may call other stored routines.

As of MySQL 5.0.1, a stored procedure or function is associated with a particular database. This has several implications:

- When the routine is invoked, an implicit `USE `db_name`` is performed (and undone when the routine terminates). `USE` statements within stored routines are disallowed.

- You can qualify routine names with the database name. This can be used to refer to a routine that is not in the current database. For example, to invoke a stored procedure `p` or function `f` that is associated with the `test` database, you can say `CALL test.p()` or `test.f()`.

- When a database is dropped, all stored routines associated with it are dropped as well.

(In MySQL 5.0.0, stored routines are global and not associated with a database. They inherit the default database from the caller. If a `USE `db_name`` is executed within the routine, the original default database is restored upon routine exit.)

MySQL supports the very useful extension that allows the use of regular `SELECT` statements (that is, without using cursors or local variables) inside a stored procedure. The result set of such a query is simply sent directly to the client. Multiple `SELECT` statements generate multiple result sets, so the client must use a MySQL client library that supports multiple result sets. This means the client must use a client library from a version of MySQL at least as recent as 4.1. The client should also specify the `CLIENT_MULTI_STATEMENTS` option when it connects. For C programs, this can be done with the `mysql_real_connect()` C API function (see Section 22.2.3.51, “`mysql_real_connect()`”).

The following sections describe the syntax used to create, alter, drop, and invoke stored procedures and functions.

### 17.2.1. `CREATE PROCEDURE` and `CREATE FUNCTION` Syntax

    CREATE
        [DEFINER = { user | CURRENT_USER }]
        PROCEDURE sp_name ([proc_parameter[,...]])
        [characteristic ...] routine_body

    CREATE
        [DEFINER = { user | CURRENT_USER }]
        FUNCTION sp_name ([func_parameter[,...]])
        RETURNS type
        [characteristic ...] routine_body

    proc_parameter:
        [ IN | OUT | INOUT ] param_name type

    func_parameter:
        param_name type

    type:
        Any valid MySQL data type

    characteristic:
        LANGUAGE SQL
      | [NOT] DETERMINISTIC
      | { CONTAINS SQL | NO SQL | READS SQL DATA | MODIFIES SQL DATA }
      | SQL SECURITY { DEFINER | INVOKER }
      | COMMENT 'string'

    routine_body:
        Valid SQL procedure statement

These statements create stored routines. As of MySQL 5.0.3, to use them, it is necessary to have the `CREATE ROUTINE` privilege. If binary logging is enabled, these statements might may also require the `SUPER` privilege, as described in Section 17.4, “Binary Logging of Stored Routines and Triggers”. MySQL automatically grants the `ALTER ROUTINE` and `EXECUTE` privileges to the routine creator.

By default, the routine is associated with the default database. To associate the routine explicitly with a given database, specify the name as `db_name.sp_name` when you create it.

If the routine name is the same as the name of a built-in SQL function, you must use a space between the name and the following parenthesis when defining the routine, or a syntax error occurs. This is also true when you invoke the routine later. For this reason, we suggest that it is better to avoid re-using the names of existing SQL functions for your own stored routines.

The `IGNORE_SPACE` SQL mode applies to built-in functions, not to stored routines. it is always allowable to have spaces after a routine name, regardless of whether `IGNORE_SPACE` is enabled.

The parameter list enclosed within parentheses must always be present. If there are no parameters, an empty parameter list of `()` should be used. Each parameter is an `IN` parameter by default. To specify otherwise for a parameter, use the keyword `OUT` or `INOUT` before the parameter name.

Note: Specifying a parameter as `IN`, `OUT`, or `INOUT` is valid only for a `PROCEDURE`. (`FUNCTION` parameters are always regarded as `IN` parameters.)

Each parameter can be declared to use any valid data type, except that the `COLLATE` attribute cannot be used.

The `RETURNS` clause may be specified only for a `FUNCTION`, for which it is mandatory. It indicates the return type of the function, and the function body must contain a `RETURN `value`` statement.

The `routine_body` consists of a valid SQL procedure statement. This can be a simple statement such as `SELECT` or `INSERT`, or it can be a compound statement written using `BEGIN` and `END`. Compound statement syntax is described in Section 17.2.5, “`BEGIN ... END` Compound Statement Syntax”. Compound statements can contain declarations, loops, and other control structure statements. The syntax for these statements is described later in this chapter. See, for example, Section 17.2.6, “`DECLARE` Statement Syntax”, and Section 17.2.10, “Flow Control Constructs”. Some statements are not allowed in stored routines; see Section I.1, “Restrictions on Stored Routines and Triggers”.

The `CREATE FUNCTION` statement was used in earlier versions of MySQL to support UDFs (user-defined functions). See Section 24.2, “Adding New Functions to MySQL”. UDFs continue to be supported, even with the existence of stored functions. A UDF can be regarded as an external stored function. However, do note that stored functions share their namespace with UDFs.

A procedure or function is considered “deterministic” if it always produces the same result for the same input parameters, and “not deterministic” otherwise. If neither `DETERMINISTIC` nor `NOT DETERMINISTIC` is given in the routine definition, the default is `NOT DETERMINISTIC`.

For replication purposes, use of the `NOW()` function (or its synonyms) or `RAND()` does not necessarily make a routine non-deterministic. For `NOW()`, the binary log includes the timestamp and replicates correctly. `RAND()` also replicates correctly as long as it is invoked only once within a routine. (You can consider the routine execution timestamp and random number seed as implicit inputs that are identical on the master and slave.)

Currently, the `DETERMINISTIC` characteristic is accepted, but not yet used by the optimizer. However, if binary logging is enabled, this characteristic affects which routine definitions MySQL accepts. See Section 17.4, “Binary Logging of Stored Routines and Triggers”.

Several characteristics provide information about the nature of data use by the routine. `CONTAINS SQL` indicates that the routine does not contain statements that read or write data. `NO SQL` indicates that the routine contains no SQL statements. `READS SQL DATA` indicates that the routine contains statements that read data, but not statements that write data. `MODIFIES SQL DATA` indicates that the routine contains statements that may write data. `CONTAINS SQL` is the default if none of these characteristics is given explicitly. These characteristics are advisory only. The server does not use them to constrain what kinds of statements a routine will be allowed to execute.

The `SQL SECURITY` characteristic can be used to specify whether the routine should be executed using the permissions of the user who creates the routine or the user who invokes it. The default value is `DEFINER`. This feature is new in SQL:2003. The creator or invoker must have permission to access the database with which the routine is associated. As of MySQL 5.0.3, it is necessary to have the `EXECUTE` privilege to be able to execute the routine. The user that must have this privilege is either the definer or invoker, depending on how the `SQL SECURITY` characteristic is set.

The optional `DEFINER` clause specifies the MySQL account to be used when checking access privileges at routine execution time for routines that have the `SQL SECURITY DEFINER` characteristic. The `DEFINER` clause was added in MySQL 5.0.20.

If a `user` value is given, it should be a MySQL account in `'`user_name`'@'`host_name`'` format (the same format used in the `GRANT` statement). The `user_name` and `host_name` values both are required. `CURRENT_USER` also can be given as `CURRENT_USER()`. The default `DEFINER` value is the user who executes the `CREATE PROCEDURE` or `CREATE FUNCTION` or statement. (This is the same as `DEFINER = CURRENT_USER`.)

If you specify the `DEFINER` clause, you cannot set the value to any account but your own unless you have the `SUPER` privilege. These rules determine the legal `DEFINER` user values:

- If you do not have the `SUPER` privilege, the only legal `user` value is your own account, either specified literally or by using `CURRENT_USER`. You cannot set the definer to some other account.

- If you have the `SUPER` privilege, you can specify any syntactically legal account name. If the account does not actually exist, a warning is generated.

  Although it is possible to create routines with a non-existent `DEFINER` value, an error occurs if the routine executes with definer privileges but the definer does not exist at execution time.

MySQL stores the `sql_mode` system variable setting that is in effect at the time a routine is created, and always executes the routine with this setting in force.

When the routine is invoked, an implicit `USE `db_name`` is performed (and undone when the routine terminates). `USE` statements within stored routines are disallowed.

As of MySQL 5.0.18, the server uses the data type of a routine parameter or function return value as follows. These rules also apply to local routine variables created with the `DECLARE` statement (Section 17.2.7.1, “`DECLARE` Local Variables”).

- Assignments are checked for data type mismatches and overflow. Conversion and overflow problems result in warnings, or errors in strict mode.

- For character data types, if there is a `CHARACTER SET` clause in the declaration, the specified character set and its default collation are used. If there is no such clause, the database character set and collation are used. (These are given by the values of the `character_set_database` and `collation_database` system variables.)

- Only scalar values can be assigned to parameters or variables. For example, a statement such as `SET x = (SELECT 1, 2)` is invalid.

Before MySQL 5.0.18, parameters, return values, and local variables are treated as items in expressions, and are subject to automatic (silent) conversion and truncation. Stored functions ignore the `sql_mode` setting.

The `COMMENT` clause is a MySQL extension, and may be used to describe the stored routine. This information is displayed by the `SHOW CREATE PROCEDURE` and `SHOW CREATE FUNCTION` statements.

MySQL allows routines to contain DDL statements, such as `CREATE` and `DROP`. MySQL also allows stored procedures (but not stored functions) to contain SQL transaction statements such as `COMMIT`. Stored functions may not contain statements that do explicit or implicit commit or rollback. Support for these statements is not required by the SQL standard, which states that each DBMS vendor may decide whether to allow them.

Stored routines cannot use `LOAD DATA INFILE`.

Statements that return a result set cannot be used within a stored function. This includes `SELECT` statements that do not use `INTO` to fetch column values into variables, `SHOW` statements, and other statements such as `EXPLAIN`. For statements that can be determined at function definition time to return a result set, a `Not allowed to return a result set from a function` error occurs (`ER_SP_NO_RETSET_IN_FUNC`). For statements that can be determined only at runtime to return a result set, a `PROCEDURE %s can't return a result set in the given context` error occurs (`ER_SP_BADSELECT`).

Note: Before MySQL 5.0.10, stored functions created with `CREATE FUNCTION` must not contain references to tables, with limited exceptions. They may include some `SET` statements that contain table references, for example `SET a:= (SELECT MAX(id) FROM t)`, and `SELECT` statements that fetch values directly into variables, for example `SELECT i INTO var1 FROM t`.

The following is an example of a simple stored procedure that uses an `OUT` parameter. The example uses the mysql client `delimiter` command to change the statement delimiter from `;` to `//` while the procedure is being defined. This allows the `;` delimiter used in the procedure body to be passed through to the server rather than being interpreted by mysql itself.

    mysql> delimiter //

    mysql> CREATE PROCEDURE simpleproc (OUT param1 INT)
        -> BEGIN
        ->   SELECT COUNT(*) INTO param1 FROM t;
        -> END;
        -> //
    Query OK, 0 rows affected (0.00 sec)

    mysql> delimiter ;

    mysql> CALL simpleproc(@a);
    Query OK, 0 rows affected (0.00 sec)

    mysql> SELECT @a;
    +------+
    | @a   |
    +------+
    | 3    |
    +------+
    1 row in set (0.00 sec)

When using the `delimiter` command, you should avoid the use of the backslash (‘`\`’) character because that is the escape character for MySQL.

The following is an example of a function that takes a parameter, performs an operation using an SQL function, and returns the result. In this case, it is unnecessary to use `delimiter` because the function definition contains no internal `;` statement delimiters:

    mysql> CREATE FUNCTION hello (s CHAR(20)) RETURNS CHAR(50)
        -> RETURN CONCAT('Hello, ',s,'!');
    Query OK, 0 rows affected (0.00 sec)

    mysql> SELECT hello('world');
    +----------------+
    | hello('world') |
    +----------------+
    | Hello, world!  |
    +----------------+
    1 row in set (0.00 sec)

A stored function returns a value of the data type specified in its `RETURNS` clause. If the `RETURN` statement returns a value of a different type, the value is coerced to the proper type. For example, if a function returns an `ENUM` or `SET` value, but the `RETURN` statement returns an integer, the value returned from the function is the string for the corresponding `ENUM` member of set of `SET` members.

### 17.2.2. `ALTER PROCEDURE` and `ALTER FUNCTION` Syntax

    ALTER {PROCEDURE | FUNCTION} sp_name [characteristic ...]

    characteristic:
        { CONTAINS SQL | NO SQL | READS SQL DATA | MODIFIES SQL DATA }
      | SQL SECURITY { DEFINER | INVOKER }
      | COMMENT 'string'

This statement can be used to change the characteristics of a stored procedure or function. As of MySQL 5.0.3, you must have the `ALTER ROUTINE` privilege for the routine. (That privilege is granted automatically to the routine creator.) If binary logging is enabled, this statement might also require the `SUPER` privilege, as described in Section 17.4, “Binary Logging of Stored Routines and Triggers”.

More than one change may be specified in an `ALTER PROCEDURE` or `ALTER FUNCTION` statement.

### 17.2.3. `DROP PROCEDURE` and `DROP FUNCTION` Syntax

    DROP {PROCEDURE | FUNCTION} [IF EXISTS] sp_name

This statement is used to drop a stored procedure or function. That is, the specified routine is removed from the server. As of MySQL 5.0.3, you must have the `ALTER ROUTINE` privilege for the routine. (That privilege is granted automatically to the routine creator.)

The `IF EXISTS` clause is a MySQL extension. It prevents an error from occurring if the procedure or function does not exist. A warning is produced that can be viewed with `SHOW WARNINGS`.

### 17.2.4. `CALL` Statement Syntax

    CALL sp_name([parameter[,...]])

The `CALL` statement invokes a procedure that was defined previously with `CREATE PROCEDURE`.

`CALL` can pass back values to its caller using parameters that are declared as `OUT` or `INOUT` parameters. It also “returns” the number of rows affected, which a client program can obtain at the SQL level by calling the `ROW_COUNT()` function and from C by calling the `mysql_affected_rows()` C API function.

### 17.2.5. `BEGIN ... END` Compound Statement Syntax

    [begin_label:] BEGIN
        [statement_list]
    END [end_label]

`BEGIN ... END` syntax is used for writing compound statements, which can appear within stored routines and triggers. A compound statement can contain multiple statements, enclosed by the `BEGIN` and `END` keywords. `statement_list` represents a list of one or more statements. Each statement within `statement_list` must be terminated by a semicolon (`;`) statement delimiter. Note that `statement_list` is optional, which means that the empty compound statement (`BEGIN END`) is legal.

Use of multiple statements requires that a client is able to send statement strings containing the `;` statement delimiter. This is handled in the mysql command-line client with the `delimiter` command. Changing the `;` end-of-statement delimiter (for example, to `//`) allows `;` to be used in a routine body. For an example, see Section 17.2.1, “`CREATE PROCEDURE` and `CREATE FUNCTION` Syntax”.

A compound statement can be labeled. `end_label` cannot be given unless `begin_label` also is present. If both are present, they must be the same.

The optional `[NOT] ATOMIC` clause is not yet supported. This means that no transactional savepoint is set at the start of the instruction block and the `BEGIN` clause used in this context has no effect on the current transaction.

### 17.2.6. `DECLARE` Statement Syntax

The `DECLARE` statement is used to define various items local to a routine:

- Local variables. See Section 17.2.7, “Variables in Stored Routines”.

- Conditions and handlers. See Section 17.2.8, “Conditions and Handlers”.

- Cursors. See Section 17.2.9, “Cursors”.

The `SIGNAL` and `RESIGNAL` statements are not currently supported.

`DECLARE` is allowed only inside a `BEGIN ... END` compound statement and must be at its start, before any other statements.

Declarations must follow a certain order. Cursors must be declared before declaring handlers, and variables and conditions must be declared before declaring either cursors or handlers.

### 17.2.7. Variables in Stored Routines

You may declare and use variables within a routine.

#### 17.2.7.1. `DECLARE` Local Variables

    DECLARE var_name[,...] type [DEFAULT value]

This statement is used to declare local variables. To provide a default value for the variable, include a `DEFAULT` clause. The value can be specified as an expression; it need not be a constant. If the `DEFAULT` clause is missing, the initial value is `NULL`.

Local variables are treated like routine parameters with respect to data type and overflow checking. See Section 17.2.1, “`CREATE PROCEDURE` and `CREATE FUNCTION` Syntax”.

The scope of a local variable is within the `BEGIN ... END` block where it is declared. The variable can be referred to in blocks nested within the declaring block, except those blocks that declare a variable with the same name.

#### 17.2.7.2. Variable `SET` Statement

    SET var_name = expr [, var_name = expr] ...

The `SET` statement in stored routines is an extended version of the general `SET` statement. Referenced variables may be ones declared inside a routine, or global system variables.

The `SET` statement in stored routines is implemented as part of the pre-existing `SET` syntax. This allows an extended syntax of `SET a=x, b=y, ...` where different variable types (locally declared variables and global and session server variables) can be mixed. This also allows combinations of local variables and some options that make sense only for system variables; in that case, the options are recognized but ignored.

#### 17.2.7.3. `SELECT ... INTO` Statement

    SELECT col_name[,...] INTO var_name[,...] table_expr

This `SELECT` syntax stores selected columns directly into variables. Therefore, only a single row may be retrieved.

    SELECT id,data INTO x,y FROM test.t1 LIMIT 1;

User variable names are not case sensitive. See Section 9.3, “User-Defined Variables”.

Important: SQL variable names should not be the same as column names. If an SQL statement, such as a `SELECT ... INTO` statement, contains a reference to a column and a declared local variable with the same name, MySQL currently interprets the reference as the name of a variable. For example, in the following statement, `xname` is interpreted as a reference to the `xname` variable rather than the `xname` column:

    CREATE PROCEDURE sp1 (x VARCHAR(5))
      BEGIN
        DECLARE xname VARCHAR(5) DEFAULT 'bob';
        DECLARE newname VARCHAR(5);
        DECLARE xid INT;

        SELECT xname,id INTO newname,xid
          FROM table1 WHERE xname = xname;
        SELECT newname;
      END;

When this procedure is called, the `newname` variable returns the value `'bob'` regardless of the value of the `table1.xname` column.

See also Section I.1, “Restrictions on Stored Routines and Triggers”.

### 17.2.8. Conditions and Handlers

Certain conditions may require specific handling. These conditions can relate to errors, as well as to general flow control inside a routine.

#### 17.2.8.1. `DECLARE` Conditions

    DECLARE condition_name CONDITION FOR condition_value

    condition_value:
        SQLSTATE [VALUE] sqlstate_value
      | mysql_error_code

This statement specifies conditions that need specific handling. It associates a name with a specified error condition. The name can subsequently be used in a `DECLARE HANDLER` statement. See Section 17.2.8.2, “`DECLARE` Handlers”.

A `condition_value` can be an SQLSTATE value or a MySQL error code.

#### 17.2.8.2. `DECLARE` Handlers

    DECLARE handler_type HANDLER FOR condition_value[,...] statement

    handler_type:
        CONTINUE
      | EXIT
      | UNDO

    condition_value:
        SQLSTATE [VALUE] sqlstate_value
      | condition_name
      | SQLWARNING
      | NOT FOUND
      | SQLEXCEPTION
      | mysql_error_code

The `DECLARE ... HANDLER` statement specifies handlers that each may deal with one or more conditions. If one of these conditions occurs, the specified `statement` is executed. `statement` can be a simple statement (for example, `SET `var_name` = `value``), or it can be a compound statement written using `BEGIN` and `END` (see Section 17.2.5, “`BEGIN ... END` Compound Statement Syntax”).

For a `CONTINUE` handler, execution of the current routine continues after execution of the handler statement. For an `EXIT` handler, execution terminates for the `BEGIN ... END` compound statement in which the handler is declared. (This is true even if the condition occurs in an inner block.) The `UNDO` handler type statement is not yet supported.

If a condition occurs for which no handler has been declared, the default action is `EXIT`.

A `condition_value` can be any of the following values:

- An SQLSTATE value or a MySQL error code.

- A condition name previously specified with `DECLARE ... CONDITION`. See Section 17.2.8.1, “`DECLARE` Conditions”.

- `SQLWARNING` is shorthand for all SQLSTATE codes that begin with `01`.

- `NOT FOUND` is shorthand for all SQLSTATE codes that begin with `02`.

- `SQLEXCEPTION` is shorthand for all SQLSTATE codes not caught by `SQLWARNING` or `NOT FOUND`.

Example:

    mysql> CREATE TABLE test.t (s1 int,primary key (s1));
    Query OK, 0 rows affected (0.00 sec)

    mysql> delimiter //

    mysql> CREATE PROCEDURE handlerdemo ()
        -> BEGIN
        ->   DECLARE CONTINUE HANDLER FOR SQLSTATE '23000' SET @x2 = 1;
        ->   SET @x = 1;
        ->   INSERT INTO test.t VALUES (1);
        ->   SET @x = 2;
        ->   INSERT INTO test.t VALUES (1);
        ->   SET @x = 3;
        -> END;
        -> //
    Query OK, 0 rows affected (0.00 sec)

    mysql> CALL handlerdemo()//
    Query OK, 0 rows affected (0.00 sec)

    mysql> SELECT @x//
        +------+
        | @x   |
        +------+
        | 3    |
        +------+
        1 row in set (0.00 sec)

The example associates a handler with SQLSTATE 23000, which occurs for a duplicate-key error. Notice that `@x` is `3`, which shows that MySQL executed to the end of the procedure. If the line `DECLARE CONTINUE HANDLER FOR SQLSTATE '23000' SET @x2 = 1;` had not been present, MySQL would have taken the default path (`EXIT`) after the second `INSERT` failed due to the `PRIMARY KEY` constraint, and `SELECT @x` would have returned `2`.

If you want to ignore a condition, you can declare a `CONTINUE` handler for it and associate it with an empty block. For example:

    DECLARE CONTINUE HANDLER FOR SQLWARNING BEGIN END;

### 17.2.9. Cursors

Simple cursors are supported inside stored procedures and functions. The syntax is as in embedded SQL. Cursors are currently asensitive, read-only, and non-scrolling. Asensitive means that the server may or may not make a copy of its result table.

Cursors must be declared before declaring handlers, and variables and conditions must be declared before declaring either cursors or handlers.

Example:

    CREATE PROCEDURE curdemo()
    BEGIN
      DECLARE done INT DEFAULT 0;
      DECLARE a CHAR(16);
      DECLARE b,c INT;
      DECLARE cur1 CURSOR FOR SELECT id,data FROM test.t1;
      DECLARE cur2 CURSOR FOR SELECT i FROM test.t2;
      DECLARE CONTINUE HANDLER FOR SQLSTATE '02000' SET done = 1;

      OPEN cur1;
      OPEN cur2;

      REPEAT
        FETCH cur1 INTO a, b;
        FETCH cur2 INTO c;
        IF NOT done THEN
           IF b < c THEN
              INSERT INTO test.t3 VALUES (a,b);
           ELSE
              INSERT INTO test.t3 VALUES (a,c);
           END IF;
        END IF;
      UNTIL done END REPEAT;

      CLOSE cur1;
      CLOSE cur2;
    END

#### 17.2.9.1. Declaring Cursors

    DECLARE cursor_name CURSOR FOR select_statement

This statement declares a cursor. Multiple cursors may be declared in a routine, but each cursor in a given block must have a unique name.

The `SELECT` statement cannot have an `INTO` clause.

#### 17.2.9.2. Cursor `OPEN` Statement

    OPEN cursor_name

This statement opens a previously declared cursor.

#### 17.2.9.3. Cursor `FETCH` Statement

    FETCH cursor_name INTO var_name [, var_name] ...

This statement fetches the next row (if a row exists) using the specified open cursor, and advances the cursor pointer.

#### 17.2.9.4. Cursor `CLOSE` Statement

    CLOSE cursor_name

This statement closes a previously opened cursor.

If not closed explicitly, a cursor is closed at the end of the compound statement in which it was declared.

### 17.2.10. Flow Control Constructs

The `IF`, `CASE`, `LOOP`, `WHILE`, `REPLACE` `ITERATE`, and `LEAVE` constructs are fully implemented.

Many of these constructs contain other statements, as indicated by the grammer specifications in the following sections. Such constructs may be nested. For example, an `IF` statement might contain a `WHILE` loop, which itself contains a `CASE` statement.

`FOR` loops are not currently supported.

#### 17.2.10.1. `IF` Statement

    IF search_condition THEN statement_list
        [ELSEIF search_condition THEN statement_list] ...
        [ELSE statement_list]
    END IF

`IF` implements a basic conditional construct. If the `search_condition` evaluates to true, the corresponding SQL statement list is executed. If no `search_condition` matches, the statement list in the `ELSE` clause is executed. Each `statement_list` consists of one or more statements.

Note: There is also an `IF()` function, which differs from the `IF` statement described here. See Section 12.2, “Control Flow Functions”.

#### 17.2.10.2. `CASE` Statement

    CASE case_value
        WHEN when_value THEN statement_list
        [WHEN when_value THEN statement_list] ...
        [ELSE statement_list]
    END CASE

Or:

    CASE
        WHEN search_condition THEN statement_list
        [WHEN search_condition THEN statement_list] ...
        [ELSE statement_list]
    END CASE

The `CASE` statement for stored routines implements a complex conditional construct. If a `search_condition` evaluates to true, the corresponding SQL statement list is executed. If no search condition matches, the statement list in the `ELSE` clause is executed. Each `statement_list` consists of one or more statements.

Note: The syntax of the `CASE` statement shown here for use inside stored routines differs slightly from that of the SQL `CASE` expression described in Section 12.2, “Control Flow Functions”. The `CASE` statement cannot have an `ELSE NULL` clause, and it is terminated with `END CASE` instead of `END`.

#### 17.2.10.3. `LOOP` Statement

    [begin_label:] LOOP
        statement_list
    END LOOP [end_label]

`LOOP` implements a simple loop construct, enabling repeated execution of the statement list, which consists of one or more statements. The statements within the loop are repeated until the loop is exited; usually this is accomplished with a `LEAVE` statement.

A `LOOP` statement can be labeled. `end_label` cannot be given unless `begin_label` also is present. If both are present, they must be the same.

#### 17.2.10.4. `LEAVE` Statement

    LEAVE label

This statement is used to exit any labeled flow control construct. It can be used within `BEGIN ... END` or loop constructs (`LOOP`, `REPEAT`, `WHILE`).

#### 17.2.10.5. `ITERATE` Statement

    ITERATE label

`ITERATE` can appear only within `LOOP`, `REPEAT`, and `WHILE` statements. `ITERATE` means “do the loop again.”

Example:

    CREATE PROCEDURE doiterate(p1 INT)
    BEGIN
      label1: LOOP
        SET p1 = p1 + 1;
        IF p1 < 10 THEN ITERATE label1; END IF;
        LEAVE label1;
      END LOOP label1;
      SET @x = p1;
    END

#### 17.2.10.6. `REPEAT` Statement

    [begin_label:] REPEAT
        statement_list
    UNTIL search_condition
    END REPEAT [end_label]

The statement list within a `REPEAT` statement is repeated until the `search_condition` is true. Thus, a `REPEAT` always enters the loop at least once. `statement_list` consists of one or more statements.

A `REPEAT` statement can be labeled. `end_label` cannot be given unless `begin_label` also is present. If both are present, they must be the same.

Example:

    mysql> delimiter //

    mysql> CREATE PROCEDURE dorepeat(p1 INT)
        -> BEGIN
        ->   SET @x = 0;
        ->   REPEAT SET @x = @x + 1; UNTIL @x > p1 END REPEAT;
        -> END
        -> //
    Query OK, 0 rows affected (0.00 sec)

    mysql> CALL dorepeat(1000)//
    Query OK, 0 rows affected (0.00 sec)

    mysql> SELECT @x//
    +------+
    | @x   |
    +------+
    | 1001 |
    +------+
    1 row in set (0.00 sec)

#### 17.2.10.7. `WHILE` Statement

    [begin_label:] WHILE search_condition DO
        statement_list
    END WHILE [end_label]

The statement list within a `WHILE` statement is repeated as long as the `search_condition` is true. `statement_list` consists of one or more statements.

A `WHILE` statement can be labeled. `end_label` cannot be given unless `begin_label` also is present. If both are present, they must be the same.

Example:

    CREATE PROCEDURE dowhile()
    BEGIN
      DECLARE v1 INT DEFAULT 5;

      WHILE v1 > 0 DO
        ...
        SET v1 = v1 - 1;
      END WHILE;
    END

## 17.3. Stored Procedures, Functions, Triggers, and Replication: Frequently Asked Questions

- Do MySQL 5.0 stored procedures and functions work with replication?

  Yes, standard actions carried out in stored procedures and functions are replicated from a master MySQL server to a slave server. There are a few limitations that are described in detail in Section 17.4, “Binary Logging of Stored Routines and Triggers”.

- Are stored procedures and functions created on a master server replicated to a slave?

  Yes, creation of stored procedures and functions carried out through normal DDL statements on a master server are replicated to a slave, so the objects will exist on both servers. `ALTER` and `DROP` statements for stored procedures and functions are also replicated.

- How are actions that take place inside stored procedures and functions replicated?

  MySQL records each DML event that occurs in a stored procedure and replicates those individual actions to a slave server. The actual calls made to execute stored procedures are not replicated.

  Stored functions that change data are logged as function invocations, not as the DML events that occur inside each function.

- Are there special security requirements for using stored procedures and functions together with replication?

  Yes. Because a slave server has authority to execute any statement read from a master's binary log, special security constraints exist for using stored functions with replication. If replication or binary logging in general (for the purpose of point-in-time recovery) is active, then MySQL DBAs have two security options open to them:

  - Any user wishing to create stored functions must be granted the `SUPER` privilege.

  - Alternatively, a DBA can set the `log_bin_trust_function_creators` system variable to 1, which enables anyone with the standard `CREATE ROUTINE` privilege to create stored functions.

  Note: Before MySQL 5.0.16, these restrictions also apply to stored procedures and the system variable is named `log_bin_trust_routine_creators`.

- What limitations exist for replicating stored procedure and function actions?

  Non-deterministic (random) or time-based actions embedded in stored procedures may not replicate properly. By their very nature, randomly produced results are not predictable and cannot be exactly reproduced, and therefore, random actions replicated to a slave will not mirror those performed on a master. Note that declaring stored functions to be `DETERMINISTIC` or setting the `log_bin_trust_function_creators` system variable to 0 will not allow random-valued operations to be invoked.

  In addition, time-based actions cannot be reproduced on a slave because the timing of such actions in a stored procedure is not reproducible through the binary log used for replication. It records only DML events and does not factor in timing constraints.

  Finally, non-transactional tables for which errors occur during large DML actions (such as bulk inserts) may experience replication issues in that a master may be partially updated from DML activity, but no updates are done to the slave because of the errors that occurred. A workaround is for a function's DML actions to be carried out with the `IGNORE` keyword so that updates on the master that cause errors are ignored and updates that do not cause errors are replicated to the slave.

- Do the preceding limitations affect MySQL's ability to do point-in-time recovery?

  The same limitations that affect replication do affect point-in-time recovery.

- What will MySQL do to correct the aforementioned limitations?

  A future release of MySQL is expected to feature a choice in how replication should be handled:

  - Statement-based replication (current implementation).

  - Row-level replication (that will solve all the limitations described earlier).

- Do triggers work with replication?

  Triggers and replication in MySQL 5.0 work the same as in most other database engines: Actions carried out through triggers on a master are not replicated to a slave server. Instead, triggers that exist on tables that reside on a MySQL master server need to be created on the corresponding tables on any MySQL slave servers so that the triggers activate on the slaves as well as the master.

- How are actions carried out through triggers on a master replicated to a slave?

  First, the triggers that exist on a master must be re-created on the slave server. Once this is done, the replication flow works as any other standard DML statement that participates in replication. For example, consider a table `EMP` that has an `AFTER` insert trigger, which exists on a master MySQL server. The same `EMP` table and `AFTER` insert trigger exist on the slave server as well. The replication flow would be:

  1. An `INSERT` statement is made to `EMP`.

  2. The `AFTER` trigger on `EMP` activates.

  3. The `INSERT` statement is written to the binary log.

  4. The replication slave picks up the `INSERT` statement to `EMP` and executes it.

  5. The `AFTER` trigger on `EMP` that exists on the slave activates.

## 17.4. Binary Logging of Stored Routines and Triggers

The binary log contains information about SQL statements that modify database contents. This information is stored in the form of “events” that describe the modifications. The binary log has two important purposes:

- For replication, the master server sends the events contained in its binary log to its slaves, which execute those events to make the same data changes that were made on the master. See Section 6.2, “Replication Implementation Overview”.

- Certain data recovery operations require use of the binary log. After a backup file has been restored, the events in the binary log that were recorded after the backup was made are re-executed. These events bring databases up to date from the point of the backup. See Section 5.10.2.2, “Using Backups for Recovery”.

This section describes the development of binary logging in MySQL 5.0 with respect to stored routines (procedures and functions) and triggers. The discussion first summarizes the changes that have taken place in the logging implementation, and then states the current conditions that the implementation places on the use of stored routines. Finally, implementation details are given that provide information about when and why various changes were made. These details show how several aspects of the current logging behavior were implemented in response to shortcomings identified in earlier versions.

In general, the issues described here result from the fact that binary logging occurs at the SQL statement level. A future MySQL release is expected to implement row-level binary logging, which specifies the changes to make to individual rows as a result of executing SQL statements.

Unless noted otherwise, the remarks here assume that you have enabled binary logging by starting the server with the `--log-bin` option. (See Section 5.12.3, “The Binary Log”.) If the binary log is not enabled, replication is not possible, nor is the binary log available for data recovery.

The development of stored routine logging in MySQL 5.0 can be summarized as follows:

- Before MySQL 5.0.6: In the initial implementation of stored routine logging, statements that create stored routines and `CALL` statements are not logged. These omissions can cause problems for replication and data recovery.

- MySQL 5.0.6: Statements that create stored routines and `CALL` statements are logged. Stored function invocations are logged when they occur in statements that update data (because those statements are logged). However, function invocations are not logged when they occur in statements such as `SELECT` that do not change data, even if a data change occurs within a function itself; this can cause problems. Under some circumstances, functions and procedures can have different effects if executed at different times or on different (master and slave) machines, and thus can be unsafe for data recovery or replication. To handle this, measures are implemented to allow identification of safe routines and to prevent creation of unsafe routines except by users with sufficient privileges.

- MySQL 5.0.12: For stored functions, when a function invocation that changes data occurs within a non-logged statement such as `SELECT`, the server logs a `DO `func_name`()` statement that invokes the function so that the function gets executed during data recovery or replication to slave servers. For stored procedures, the server does not log `CALL` statements. Instead, it logs individual statements within a procedure that are executed as a result of a `CALL`. This eliminates problems that may occur when a procedure would follow a different execution path on a slave than on the master.

- MySQL 5.0.16: The procedure logging changes made in 5.0.12 allow the conditions on unsafe routines to be relaxed for stored procedures. Consequently, the user interface for controlling these conditions is revised to apply only to functions. Procedure creators are no longer bound by them.

- MySQL 5.0.17: Logging of stored functions as `DO `func_name`()` statements (per the changes made in 5.0.12) are logged as `SELECT `func_name`()` statements instead for better control over error checking.

As a consequence of the preceding changes, the following conditions currently apply to stored function creation when binary logging is enabled. These conditions do not apply to stored procedure creation.

- To create or alter a stored function, you must have the `SUPER` privilege, in addition to the `CREATE ROUTINE` or `ALTER ROUTINE` privilege that is normally required.

- When you create a stored function, you must declare either that it is deterministic or that it does not modify data. Otherwise, it may be unsafe for data recovery or replication. Two sets of function characteristics apply here:

  - The `DETERMINISTIC` and `NOT DETERMINISTIC` characteristics indicate whether a function always produces the same result for given inputs. The default is `NOT DETERMINISTIC` if neither characteristic is given, so you must specify `DETERMINISTIC` explicitly to declare that a function is deterministic.

    Use of the `NOW()` function (or its synonyms) or `RAND()` does not necessarily make a function non-deterministic. For `NOW()`, the binary log includes the timestamp and replicates correctly. `RAND()` also replicates correctly as long as it is invoked only once within a function. (You can consider the function execution timestamp and random number seed as implicit inputs that are identical on the master and slave.)

    `SYSDATE()` is not affected by the timestamps in the binary log, so it causes stored routines to be non-deterministic if statement-based logging is used. This does not occur if the server is started with the `--sysdate-is-now` option to cause `SYSDATE()` to be an alias for `NOW()`.

  - The `CONTAINS SQL`, `NO SQL`, `READS SQL DATA`, and `MODIFIES SQL DATA` characteristics provide information about whether the function reads or writes data. Either `NO SQL` or `READS SQL DATA` indicates that a function does not change data, but you must specify one of these explicitly because the default is `CONTAINS SQL` if no characteristic is given.

  By default, for a `CREATE FUNCTION` statement to be accepted, `DETERMINISTIC` or one of `NO SQL` and `READS SQL DATA` must be specified explicitly. Otherwise an error occurs:

      ERROR 1418 (HY000): This function has none of DETERMINISTIC, NO SQL,
      or READS SQL DATA in its declaration and binary logging is enabled
      (you *might* want to use the less safe log_bin_trust_function_creators
      variable)

  Assessment of the nature of a function is based on the “honesty” of the creator: MySQL does not check that a function declared `DETERMINISTIC` contains no statements that produce non-deterministic results.

- To relax the preceding conditions on function creation (that you must have the `SUPER` privilege and that a function must be declared deterministic or to not modify data), set the global `log_bin_trust_function_creators` system variable to 1. By default, this variable has a value of 0, but you can change it like this:

      mysql> SET GLOBAL log_bin_trust_function_creators = 1;

  You can also set this variable by using the `--log-bin-trust-function-creators` option when starting the server.

  If binary logging is not enabled, `log_bin_trust_function_creators` does not apply and `SUPER` is not required for routine creation.

Triggers are similar to stored functions, so the preceding remarks regarding functions also apply to triggers with the following exception: `CREATE TRIGGER` does not have an optional `DETERMINISTIC` characteristic, so triggers are assumed to be always deterministic. However, this assumption might in some cases be invalid. For example, the `UUID()` function is non-deterministic (and does not replicate). You should be careful about using such functions in triggers.

Triggers can update tables (as of MySQL 5.0.10), so error messages similar to those for stored functions occur with `CREATE TRIGGER` if you do not have the `SUPER` privilege and `log_bin_trust_function_creators` is 0.

The rest of this section provides details on the development of stored routine logging. Some of these details give additional background on the rationale for the current logging-related conditions on stored routine use.

Routine logging before MySQL 5.0.6: Statements that create and use stored routines are not written to the binary log, but statements invoked within stored routines are logged. Suppose that you issue the following statements:

    CREATE PROCEDURE mysp INSERT INTO t VALUES(1);
    CALL mysp();

For this example, only the `INSERT` statement appears in the binary log. The `CREATE PROCEDURE` and `CALL` statements do not appear. The absence of routine-related statements in the binary log means that stored routines are not replicated correctly. It also means that for a data recovery operation, re-executing events in the binary log does not recover stored routines.

Routine logging changes in MySQL 5.0.6: To address the absence of logging for stored routine creation and `CALL` statements (and the consequent replication and data recovery concerns), the characteristics of binary logging for stored routines were changed as described here. (Some of the items in the following list point out issues that are dealt with in later versions.)

- The server writes `CREATE PROCEDURE`, `CREATE FUNCTION`, `ALTER PROCEDURE`, `ALTER FUNCTION`, `DROP PROCEDURE`, and `DROP FUNCTION` statements to the binary log. Also, the server logs `CALL` statements, not the statements executed within procedures. Suppose that you issue the following statements:

      CREATE PROCEDURE mysp INSERT INTO t VALUES(1);
      CALL mysp();

  For this example, the `CREATE PROCEDURE` and `CALL` statements appear in the binary log, but the `INSERT` statement does not appear. This corrects the problem that occurred before MySQL 5.0.6 such that only the `INSERT` was logged.

- Logging `CALL` statements has a security implication for replication, which arises from two factors:

  - It is possible for a procedure to follow different execution paths on master and slave servers.

  - Statements executed on a slave are processed by the slave SQL thread which has full privileges.

  The implication is that although a user must have the `CREATE ROUTINE` privilege to create a routine, the user can write a routine containing a dangerous statement that will execute only on the slave where the statement is processed by the SQL thread that has full privileges. For example, if the master and slave servers have server ID values of 1 and 2, respectively, a user on the master server could create and invoke an unsafe procedure `unsafe_sp()` as follows:

      mysql> delimiter //
      mysql> CREATE PROCEDURE unsafe_sp ()
          -> BEGIN
          ->   IF @@server_id=2 THEN DROP DATABASE accounting; END IF;
          -> END;
          -> //
      mysql> delimiter ;
      mysql> CALL unsafe_sp();

  The `CREATE PROCEDURE` and `CALL` statements are written to the binary log, so the slave will execute them. Because the slave SQL thread has full privileges, it will execute the `DROP DATABASE` statement that drops the `accounting` database. Thus, the `CALL` statement has different effects on the master and slave and is not replication-safe.

  The preceding example uses a stored procedure, but similar problems can occur for stored functions that are invoked within statements that are written to the binary log: Function invocation has different effects on the master and slave.

  To guard against this danger for servers that have binary logging enabled, MySQL 5.0.6 introduces the requirement that stored procedure and function creators must have the `SUPER` privilege, in addition to the usual `CREATE ROUTINE` privilege that is required. Similarly, to use `ALTER PROCEDURE` or `ALTER FUNCTION`, you must have the `SUPER` privilege in addition to the `ALTER ROUTINE` privilege. Without the `SUPER` privilege, an error will occur:

      ERROR 1419 (HY000): You do not have the SUPER privilege and
      binary logging is enabled (you *might* want to use the less safe
      log_bin_trust_routine_creators variable)

  If you do not want to require routine creators to have the `SUPER` privilege (for example, if all users with the `CREATE ROUTINE` privilege on your system are experienced application developers), set the global `log_bin_trust_routine_creators` system variable to 1. You can also set this variable by using the `--log-bin-trust-routine-creators` option when starting the server. If binary logging is not enabled, `log_bin_trust_routine_creators` does not apply and `SUPER` is not required for routine creation.

- If a routine that performs updates is non-deterministic, it is not repeatable. This can have two undesirable effects:

  - It will make a slave different from the master.

  - Restored data will be different from the original data.

  To deal with these problems, MySQL enforces the following requirement: On a master server, creation and alteration of a routine is refused unless you declare the routine to be deterministic or to not modify data. Two sets of routine characteristics apply here:

  - The `DETERMINISTIC` and `NOT DETERMINISTIC` characteristics indicate whether a routine always produces the same result for given inputs. The default is `NOT DETERMINISTIC` if neither characteristic is given, so you must specify `DETERMINISTIC` explicitly to declare that a routine is deterministic.

  - The `CONTAINS SQL`, `NO SQL`, `READS SQL DATA`, and `MODIFIES SQL DATA` characteristics provide information about whether the routine reads or writes data. Either `NO SQL` or `READS SQL DATA` indicates that a routine does not change data, but you must specify one of these explicitly because the default is `CONTAINS SQL` if no characteristic is given.

  By default, for a `CREATE PROCEDURE` or `CREATE FUNCTION` statement to be accepted, `DETERMINISTIC` or one of `NO SQL` and `READS SQL DATA` must be specified explicitly. Otherwise an error occurs:

      ERROR 1418 (HY000): This routine has none of DETERMINISTIC, NO SQL,
      or READS SQL DATA in its declaration and binary logging is enabled
      (you *might* want to use the less safe log_bin_trust_routine_creators
      variable)

  If you set `log_bin_trust_routine_creators` to 1, the requirement that routines be deterministic or not modify data is dropped.

- A `CALL` statement is written to the binary log if the routine returns no error, but not otherwise. When a routine that modifies data fails, you get this warning:

      ERROR 1417 (HY000): A routine failed and has neither NO SQL nor
      READS SQL DATA in its declaration and binary logging is enabled; if
      non-transactional tables were updated, the binary log will miss their
      changes

  This logging behavior has the potential to cause problems. If a routine partly modifies a non-transactional table (such as a `MyISAM` table) and returns an error, the binary log will not reflect these changes. To protect against this, you should use transactional tables in the routine and modify the tables within transactions.

  If you use the `IGNORE` keyword with `INSERT`, `DELETE`, or `UPDATE` to ignore errors within a routine, a partial update might occur but no error will result. Such statements are logged and they replicate normally.

- Although statements normally are not written to the binary log if they are rolled back, `CALL` statements are logged even when they occur within a rolled-back transaction. This can result in a `CALL` being rolled back on the master but executed on slaves.

- If a stored function is invoked within a statement such as `SELECT` that does not modify data, execution of the function is not written to the binary log, even if the function itself modifies data. This logging behavior has the potential to cause problems. Suppose that a function `myfunc()` is defined as follows:

      CREATE FUNCTION myfunc () RETURNS INT DETERMINISTIC
      BEGIN
        INSERT INTO t (i) VALUES(1);
        RETURN 0;
      END;

  Given that definition, the following statement is not written to the binary log because it is a `SELECT`. Nevertheless, it modifies the table `t` because `myfunc()` modifies `t`:

      SELECT myfunc();

  A workaround for this problem is to invoke functions that do updates only within statements that do updates (and which therefore are written to the binary log). Note that although the `DO` statement sometimes is executed for the side effect of evaluating an expression, `DO` is not a workaround here because it is not written to the binary log.

- On slave servers, `--replicate-*-table` rules do not apply to `CALL` statements or to statements within stored routines. These statements are always replicated. If such statements contain references to tables that do not exist on the slave, they could have undesirable effects when executed on the slave.

Routine logging changes in MySQL 5.0.12: The changes in 5.0.12 address several problems that were present in earlier versions:

- Stored function invocations in non-logged statements such as `SELECT` were not being logged, even when a function itself changed data.

- Stored procedure logging at the `CALL` level could cause different effects on a master and slave if a procedure took different execution paths on the two machines.

- `CALL` statements were logged even when they occurred within a rolled-back transaction.

To deal with these issues, MySQL 5.0.12 implements the following changes to function and procedure logging:

- A stored function invocation is logged as a `DO` statement if the function changes data and occurs within a statement that would not otherwise be logged. This corrects the problem of non-replication of data changes that result from use of stored functions in non-logged statements. For example, `SELECT` statements are not written to the binary log, but a `SELECT` might invoke a stored function that makes changes. To handle this, a `DO `func_name`()` statement is written to the binary log when the given function makes a change. Suppose that the following statements are executed on the master:

      CREATE FUNCTION f1(a INT) RETURNS INT
      BEGIN
        IF (a < 3) THEN
          INSERT INTO t2 VALUES (a);
        END IF;
      END;

      CREATE TABLE t1 (a INT);
      INSERT INTO t1 VALUES (1),(2),(3);

      SELECT f1(a) FROM t1;

  When the `SELECT` statement executes, the function `f1()` is invoked three times. Two of those invocations insert a row, and MySQL logs a `DO` statement for each of them. That is, MySQL writes the following statements to the binary log:

      DO f1(1);
      DO f1(2);

  The server also logs a `DO` statement for a stored function invocation when the function invokes a stored procedure that causes an error. In this case, the server writes the `DO` statement to the log along with the expected error code. On the slave, if the same error occurs, that is the expected result and replication continues. Otherwise, replication stops.

  Note: See later in this section for changes made in MySQL 5.0.19: These logged `DO `func_name`()` statements are logged as `SELECT `func_name`()` statements instead.

- Stored procedure calls are logged at the statement level rather than at the `CALL` level. That is, the server does not log the `CALL` statement, it logs those statements within the procedure that actually execute. As a result, the same changes that occur on the master will be observed on slave servers. This eliminates the problems that could result from a procedure having different execution paths on different machines. For example, the `DROP DATABASE` problem shown earlier for the `unsafe_sp()` procedure does not occur and the routine is no longer replication-unsafe because it has the same effect on master and slave servers.

  In general, statements executed within a stored procedure are written to the binary log using the same rules that would apply were the statements to be executed in standalone fashion. Some special care is taken when logging procedure statements because statement execution within procedures is not quite the same as in non-procedure context:

  - A statement to be logged might contain references to local procedure variables. These variables do not exist outside of stored procedure context, so a statement that refers to such a variable cannot be logged literally. Instead, each reference to a local variable is replaced by this construct for logging purposes:

        NAME_CONST(var_name, var_value)

    `var_name` is the local variable name, and `var_value` is a constant indicating the value that the variable has at the time the statement is logged. `NAME_CONST()` has a value of `var_value`, and a “name” of `var_name`. Thus, if you invoke this function directly, you get a result like this:

        mysql> SELECT NAME_CONST('myname', 14);
        +--------+
        | myname |
        +--------+
        |     14 |
        +--------+

    `NAME_CONST()` allows a logged standalone statement to be executed on a slave with the same effect as the original statement that was executed on the master within a stored procedure.

  - A statement to be logged might contain references to user-defined variables. To handle this, MySQL writes a `SET` statement to the binary log to make sure that the variable exists on the slave with the same value as on the master. For example, if a statement refers to a variable `@my_var`, that statement will be preceded in the binary log by the following statement, where `value` is the value of `@my_var` on the master:

        SET @my_var = value;

  - Procedure calls can occur within a committed or rolled-back transaction. Previously, `CALL` statements were logged even if they occurred within a rolled-back transaction. As of MySQL 5.0.12, transactional context is accounted for so that the transactional aspects of procedure execution are replicated correctly. That is, the server logs those statements within the procedure that actually execute and modify data, and also logs `BEGIN`, `COMMIT`, and `ROLLBACK` statements as necessary. For example, if a procedure updates only transactional tables and is executed within a transaction that is rolled back, those updates are not logged. If the procedure occurs within a committed transaction, `BEGIN` and `COMMIT` statements are logged with the updates. For a procedure that executes within a rolled-back transaction, its statements are logged using the same rules that would apply if the statements were executed in standalone fashion:

    - Updates to transactional tables are not logged.

    - Updates to non-transactional tables are logged because rollback does not cancel them.

    - Updates to a mix of transactional and non-transactional tables are logged surrounded by `BEGIN` and `ROLLBACK` so that slaves will make the same changes and rollbacks as on the master.

- A stored procedure call is not written to the binary log at the statement level if the procedure is invoked from within a stored function. In that case, the only thing logged is the statement that invokes the function (if it occurs within a statement that is logged) or a `DO` statement (if it occurs within a statement that is not logged). For this reason, care still should be exercised in the use of stored functions that invoke a procedure, even if the procedure is otherwise safe in itself.

- Because procedure logging occurs at the statement level rather than at the `CALL` level, interpretation of the `--replicate-*-table` options is revised to apply only to stored functions. They no longer apply to stored procedures, except those procedures that are invoked from within functions.

Routine logging changes in MySQL 5.0.16: In 5.0.12, a change was introduced to log stored procedure calls at the statement level rather than at the `CALL` level. This change eliminates the requirement that procedures be identified as safe. The requirement now exists only for stored functions, because they still appear in the binary log as function invocations rather than as the statements executed within the function. To reflect the lifting of the restriction on stored procedures, the `log_bin_trust_routine_creators` system variable is renamed to `log_bin_trust_function_creators` and the `--log-bin-trust-routine-creators` server option is renamed to `--log-bin-trust-function-creators`. (For backward compatibility, the old names are recognized but result in a warning.) Error messages that now apply only to functions and not to routines in general are re-worded.

Routine logging changes in MySQL 5.0.19: In 5.0.12, a change was introduced to log a stored function invocation as `DO `func_name`()` if the invocation changes data and occurs within a non-logged statement, or if the function invokes a stored procedure that produces an error. In 5.0.19, these invocations are logged as `SELECT `func_name`()` instead. The change to `SELECT` was made because use of `DO` was found to yield insufficient control over error code checking.

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