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. By default, a 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.

The CREATE FUNCTION statement is also used in MySQL to support UDFs (user-defined functions). See Section 21.2, “Adding New Functions to MySQL”. A UDF can be regarded as an external stored function. However, do note that stored functions share their namespace with UDFs. See Section 8.2.3, “Function Name Parsing and Resolution”, for the rules describing how the server interprets references to different kinds of functions.

To invoke a stored procedure, use the CALL statement (see Section 12.2.1, “CALL Syntax”). To invoke a stored function, refer to it in an expression. The function returns a value during expression evaluation.

As of MySQL 5.0.3, to execute the CREATE PROCEDURE or CREATE FUNCTION statement, it is necessary to have the CREATE ROUTINE privilege. By default, MySQL automatically grants the ALTER ROUTINE and EXECUTE privileges to the routine creator. This behavior can be changed by disabling the automatic_sp_privileges system variable. See Section 18.2.2, “Stored Routines and MySQL Privileges”. If binary logging is enabled, the CREATE FUNCTION statement might also require the SUPER privilege, as described in Section 18.5, “Binary Logging of Stored Programs”. SUPER may also be required depending on the DEFINER value, as described later.

The DEFINER and SQL SECURITY clauses specify the security context to be used when checking access privileges at routine execution time, as described later.

If the routine name is the same as the name of a built-in SQL function, a syntax error occurs unless you use a space between the name and the following parenthesis when defining the routine or invoking it later. For this reason, avoid 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 stored 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. Parameter names are not case sensitive.

Each parameter is an IN parameter by default. To specify otherwise for a parameter, use the keyword OUT or INOUT before the parameter name.

An IN parameter passes a value into a procedure. The procedure might modify the value, but the modification is not visible to the caller when the procedure returns. An OUT parameter passes a value from the procedure back to the caller. Its initial value is NULL within the procedure, and its value is visible to the caller when the procedure returns. An INOUT parameter is initialized by the caller, can be modified by the procedure, and any change made by the procedure is visible to the caller when the procedure returns.

For each OUT or INOUT parameter, pass a user-defined variable in the CALL statement that invokes the procedure so that you can obtain its value when the procedure returns. If you are calling the procedure from within another stored procedure or function, you can also pass a routine parameter or local routine variable as an IN or INOUT parameter.

The following example shows a simple stored procedure that uses an OUT parameter:

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)

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. See Section 18.1, “Defining Stored Programs”.

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. If the RETURN statement returns a value of a different type, the value is coerced to the proper type. For example, if a function specifies an ENUM or SET value in the RETURNS clause, 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.

The following example function 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))
mysql> RETURNS CHAR(50) DETERMINISTIC
    -> 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)

Parameter types and function return types can be declared to use any valid data type, except that the COLLATE attribute cannot be used.

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 statements can contain declarations, loops, and other control structure statements. The syntax for these statements is described in Section 12.7, “MySQL Compound-Statement Syntax”.

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 perform 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.

Statements that return a result set can be used within a stored procedcure but not within a stored function. This prohibition includes SELECT statements that do not have an INTO var_list clause and other statements such as SHOW, EXPLAIN, and CHECK TABLE. 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). 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).

USE statements within stored routines are disallowed. When a routine is invoked, an implicit USE db_name is performed (and undone when the routine terminates). This causes the routine to have the given default database while it executes. References to objects in databases other than the routine default database should be qualified with the appropriate database name.

For additional information about statements that are not allowed in stored routines, see Section D.1, “Restrictions on Stored Routines and Triggers”.

For information about invoking stored procedures from within programs written in a language that has a MySQL interface, see Section 12.2.1, “CALL Syntax”.

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, regardless of the server SQL mode in effect when the routine is invoked.

The switch from the SQL mode of the invoker to that of the routine occurs after evaluation of arguments and assignment of the resulting values to routine parameters. If you define a routine in strict SQL mode but invoke it in nonstrict mode, assignment of arguments to routine parameters does not take place in strict mode. If you require that expressions passed to a routine be assigned in strict SQL mode, you should invoke the routine with strict mode in effect.

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.

A routine that contains the NOW() function (or its synonyms) or RAND() is nondeterministic, but it might still be replication-safe. For NOW(), the binary log includes the timestamp and replicates correctly. RAND() also replicates correctly as long as it is called only a single time during the execution of a routine. (You can consider the routine execution timestamp and random number seed as implicit inputs that are identical on the master and slave.)

Prior to MySQL 5.0.44, the DETERMINISTIC characteristic is accepted, but not used by the optimizer. However, if binary logging is enabled, this characteristic always affects which routine definitions MySQL accepts. See Section 18.5, “Binary Logging of Stored Programs”.

Several characteristics provide information about the nature of data use by the routine. In MySQL, 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 COMMENT characteristic 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.

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 for the DEFINER clause, 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. The definer can also be given as CURRENT_USER or 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, these rules determine the legal DEFINER user values:

Within a stored routine that is defined with the SQL SECURITY DEFINER characteristic, CURRENT_USER returns the routine's DEFINER value. For information about user auditing within stored routines, see Section 5.5.8, “Auditing MySQL Account Activity”.

Consider the following procedure, which displays a count of the number of MySQL accounts listed in the mysql.user table:

CREATE DEFINER = 'admin'@'localhost' PROCEDURE account_count()
BEGIN
  SELECT 'Number of accounts:', COUNT(*) FROM mysql.user;
END;

The procedure is assigned a DEFINER account of 'admin'@'localhost' no matter which user defines it. It executes with the privileges of that account no matter which user invokes it (because the default security characteristic is DEFINER). The procedure succeeds or fails depending on whether 'admin'@'localhost' has the EXECUTE privilege for it and the SELECT privilege for the mysql.user table.

Now suppose that the procedure is defined with the SQL SECURITY INVOKER characteristic:

CREATE DEFINER = 'admin'@'localhost' PROCEDURE account_count()
SQL SECURITY INVOKER
BEGIN
  SELECT 'Number of accounts:', COUNT(*) FROM mysql.user;
END;

The procedure still has a DEFINER of 'admin'@'localhost', but in this case, it executes with the privileges of the invoking user. Thus, the procedure succeeds or fails depending on whether the invoker has the required privileges.

As of MySQL 5.0.18, the handles the data type of a routine parameter, local routine variable created with DECLARE, or function return value as follows:

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.