15.1.17 CREATE PROCEDURE and CREATE FUNCTION Statements

CREATE
    [DEFINER = user]
    PROCEDURE [IF NOT EXISTS] sp_name ([proc_parameter[,...]])
    [characteristic ...] routine_body

CREATE
    [DEFINER = user]
    FUNCTION [IF NOT EXISTS] 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: {
    COMMENT 'string'
  | LANGUAGE SQL
  | [NOT] DETERMINISTIC
  | { CONTAINS SQL | NO SQL | READS SQL DATA | MODIFIES SQL DATA }
  | SQL SECURITY { DEFINER | INVOKER }
}

routine_body:
    Valid SQL routine statement

These statements are used to create a stored routine (a stored procedure or function). That is, the specified routine becomes known to the server. By default, a stored 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 loadable functions. See Section 15.7.4.1, “CREATE FUNCTION Statement for Loadable Functions”. A loadable function can be regarded as an external stored function. Stored functions share their namespace with loadable functions. See Section 11.2.5, “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 15.2.1, “CALL Statement”). To invoke a stored function, refer to it in an expression. The function returns a value during expression evaluation.

CREATE PROCEDURE and CREATE FUNCTION require the CREATE ROUTINE privilege. If the DEFINER clause is present, the privileges required depend on the user value, as discussed in Section 27.6, “Stored Object Access Control”. If binary logging is enabled, CREATE FUNCTION might require the SUPER privilege, as discussed in Section 27.7, “Stored Program Binary Logging”.

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 27.2.2, “Stored Routines and MySQL Privileges”.

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

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 permissible to have spaces after a stored routine name, regardless of whether IGNORE_SPACE is enabled.

IF NOT EXISTS prevents an error from occurring if there already exists a routine with the same name. This option is supported with both CREATE FUNCTION and CREATE PROCEDURE beginning with MySQL 8.0.29.

If a built-in function with the same name already exists, attempting to create a stored function with CREATE FUNCTION ... IF NOT EXISTS succeeds with a warning indicating that it has the same name as a native function; this is no different than when performing the same CREATE FUNCTION statement without specifying IF NOT EXISTS.

If a loadable function with the same name already exists, attempting to create a stored function using IF NOT EXISTS succeeds with a warning. This is the same as without specifying IF NOT EXISTS.

See Function Name Resolution, for more information.

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.

Note

Specifying a parameter as IN, OUT, or INOUT is valid only for a PROCEDURE. For a FUNCTION, parameters are always regarded as IN parameters.

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 OUT or INOUT parameter. If you are calling the procedure from within a trigger, you can also pass NEW.col_name as an OUT or INOUT parameter.

For information about the effect of unhandled conditions on procedure parameters, see Section 15.6.7.8, “Condition Handling and OUT or INOUT Parameters”.

Routine parameters cannot be referenced in statements prepared within the routine; see Section 27.8, “Restrictions on Stored Programs”.

The following example shows a simple stored procedure that, given a country code, counts the number of cities for that country that appear in the city table of the world database. The country code is passed using an IN parameter, and the city count is returned using an OUT parameter:

mysql> delimiter //

mysql> CREATE PROCEDURE citycount (IN country CHAR(3), OUT cities INT)
       BEGIN
         SELECT COUNT(*) INTO cities FROM world.city
         WHERE CountryCode = country;
       END//
Query OK, 0 rows affected (0.01 sec)

mysql> delimiter ;

mysql> CALL citycount('JPN', @cities); -- cities in Japan
Query OK, 1 row affected (0.00 sec)

mysql> SELECT @cities;
+---------+
| @cities |
+---------+
|     248 |
+---------+
1 row in set (0.00 sec)

mysql> CALL citycount('FRA', @cities); -- cities in France
Query OK, 1 row affected (0.00 sec)

mysql> SELECT @cities;
+---------+
| @cities |
+---------+
|      40 |
+---------+
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 enables the ; delimiter used in the procedure body to be passed through to the server rather than being interpreted by mysql itself. See Section 27.1, “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))
    ->   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. The COLLATE attribute can be used if preceded by a CHARACTER SET specification.

The routine_body consists of a valid SQL routine statement. This can be a simple statement such as SELECT or INSERT, or 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 15.6, “Compound Statement Syntax”. In practice, stored functions tend to use compound statements, unless the body consists of a single RETURN statement.

MySQL permits routines to contain DDL statements, such as CREATE and DROP. MySQL also permits 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 permit them.

Statements that return a result set can be used within a stored procedure 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 not permitted. When a routine is invoked, an implicit USE db_name is performed (and undone when the routine terminates). The 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 permitted in stored routines, see Section 27.8, “Restrictions on Stored Programs”.

For information about invoking stored procedures from within programs written in a language that has a MySQL interface, see Section 15.2.1, “CALL Statement”.

MySQL stores the sql_mode system variable setting in effect when a routine is created or altered, and always executes the routine with this setting in force, regardless of the current server SQL mode when the routine begins executing.

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.

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 LANGUAGE characteristic indicates the language in which the routine is written. The server ignores this characteristic; only SQL routines are supported.

A routine 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. To declare that a function is deterministic, you must specify DETERMINISTIC explicitly.

Assessment of the nature of a routine is based on the “honesty” of the creator: MySQL does not check that a routine declared DETERMINISTIC is free of statements that produce nondeterministic results. However, misdeclaring a routine might affect results or affect performance. Declaring a nondeterministic routine as DETERMINISTIC might lead to unexpected results by causing the optimizer to make incorrect execution plan choices. Declaring a deterministic routine as NONDETERMINISTIC might diminish performance by causing available optimizations not to be used.

If binary logging is enabled, the DETERMINISTIC characteristic affects which routine definitions MySQL accepts. See Section 27.7, “Stored Program Binary Logging”.

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 source and replica.)

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 is permitted to execute.

• CONTAINS SQL indicates that the routine does not contain statements that read or write data. This is the default if none of these characteristics is given explicitly. Examples of such statements are SET @x = 1 or DO RELEASE_LOCK('abc'), which execute but neither read nor write data.

• NO SQL indicates that the routine contains no SQL statements.

• READS SQL DATA indicates that the routine contains statements that read data (for example, SELECT), but not statements that write data.

• MODIFIES SQL DATA indicates that the routine contains statements that may write data (for example, INSERT or DELETE).

The SQL SECURITY characteristic can be DEFINER or INVOKER to specify the security context; that is, whether the routine executes using the privileges of the account named in the routine DEFINER clause or the user who invokes it. This account must have permission to access the database with which the routine is associated. The default value is DEFINER. The user who invokes the routine must have the EXECUTE privilege for it, as must the DEFINER account if the routine executes in definer security context.

The 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.

If the DEFINER clause is present, the user value should be a MySQL account specified as 'user_name'@'host_name', CURRENT_USER, or CURRENT_USER(). The permitted user values depend on the privileges you hold, as discussed in Section 27.6, “Stored Object Access Control”. Also see that section for additional information about stored routine security.

If the DEFINER clause is omitted, the default definer is the user who executes the CREATE PROCEDURE or CREATE FUNCTION statement. This is the same as specifying DEFINER = CURRENT_USER explicitly.

Within the body of a stored routine that is defined with the SQL SECURITY DEFINER characteristic, the CURRENT_USER function returns the routine's DEFINER value. For information about user auditing within stored routines, see Section 8.2.23, “SQL-Based Account Activity Auditing”.

Consider the following procedure, which displays a count of the number of MySQL accounts listed in the mysql.user system 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 invoker has the EXECUTE privilege for it and 'admin'@'localhost' has 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 EXECUTE privilege for it and the SELECT privilege for the mysql.user table.

By default, when a routine with the SQL SECURITY DEFINER characteristic is executed, MySQL Server does not set any active roles for the MySQL account named in the DEFINER clause, only the default roles. The exception is if the activate_all_roles_on_login system variable is enabled, in which case MySQL Server sets all roles granted to the DEFINER user, including mandatory roles. Any privileges granted through roles are therefore not checked by default when the CREATE PROCEDURE or CREATE FUNCTION statement is issued. For stored programs, if execution should occur with roles different from the default, the program body can execute SET ROLE to activate the required roles. This must be done with caution since the privileges assigned to roles can be changed.

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

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

• Only scalar values can be assigned. For example, a statement such as SET x = (SELECT 1, 2) is invalid.

• For character data types, if CHARACTER SET is included in the declaration, the specified character set and its default collation is used. If the COLLATE attribute is also present, that collation is used rather than the default collation.

  If CHARACTER SET and COLLATE are not present, the database character set and collation in effect at routine creation time are used. To avoid having the server use the database character set and collation, provide an explicit CHARACTER SET and a COLLATE attribute for character data parameters.

  If you alter the database default character set or collation, stored routines that are to use the new database defaults must be dropped and recreated.

  The database character set and collation are given by the value of the character_set_database and collation_database system variables. For more information, see Section 12.3.3, “Database Character Set and Collation”.