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

Description:

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 http://dev.mysql.com/doc/refman/5.1/en/adding-functions.html. A UDF can be regarded as an external stored function. However, do note that stored functions share their namespace with UDFs. See http://dev.mysql.com/doc/refman/5.1/en/function-resolution.html, for the rules describing how the server interprets references to different kinds of functions.

When the 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. USE statements within stored routines are disallowed.

When a stored function has been created, you invoke it by referring to it in an expression. The function returns a value during expression evaluation. When a stored procedure has been created, you invoke it by using the CALL statement (see CALL).

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. See also http://dev.mysql.com/doc/refman/5.1/en/stored-routines-privileges.html. If binary logging is enabled, the CREATE FUNCTION statement might also require the SUPER privilege, as described in http://dev.mysql.com/doc/refman/5.1/en/stored-programs-logging.html.

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, 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. Parameter names are not case sensitive.

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

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 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 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 http://dev.mysql.com/doc/refman/5.1/en/sql-syntax-compound-statements.html

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 cannot be used within a stored function. This 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).

For additional information about statements that are not allowed in stored routines, see http://dev.mysql.com/doc/refman/5.1/en/stored-program-restrictions.html .

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

MariaDB [test]> delimiter //

MariaDB [test]> CREATE PROCEDURE simpleproc (OUT param1 INT)
    -> BEGIN
    ->   SELECT COUNT(*) INTO param1 FROM t;
    -> END;
    -> //
Query OK, 0 rows affected (0.03 sec)

MariaDB [test]> delimiter ;

MariaDB [test]> CALL simpleproc(@a);
Query OK, 0 rows affected (0.00 sec)

MariaDB [test]> SELECT @a;
+------+
| @a   |
+------+
|    1 |
+------+
1 row in set (0.00 sec)

MariaDB [test]>

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 http://dev.mysql.com/doc/refman/5.1/en/stored-programs-defining.html

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

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:

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

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

MariaDB [test]>

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.

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