CREATE PROCEDURE and CREATE FUNCTION Syntax
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 28.4, "Adding New Functions to MySQL". A UDF can be regarded as an external stored function. Stored functions share their namespace with UDFs. See Section 9.2.4, "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 13.2.1, "CALL Syntax"). 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. They might also require the SUPER privilege, depending on the DEFINER value, as described later in this section. If binary logging is enabled, CREATE FUNCTION might require the SUPER privilege, as described in Section 23.7, "Binary Logging of Stored Programs".
By default, MySQL automatically grants the ALTER ROUTINE and EXECUTE privileges to the routine creator. This behavior can be changed by disabling the auto_sp_privileges system variable. See Section 23.2.2, "Stored Routines and MySQL Privileges".
The DEFINER and SQL SECURITY clasues 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.
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, pas 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 of function, you can also pass a routine parameter or local routine variable as an IN or INOUT parameter.
Routine parameters cannot be referenced in statements prepared within the routine; See Section C.1, "Restrictions on Stored Programs".
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 test0907.events_list;
-> end //
Query OK, 0 rows affected (0.00 sec)
mysql> delimiter ;
mysql> call simpleproc(@a);
Query OK, 1 row affected (0.00 sec)
mysql> select @a;
+-------+
| @a |
+-------+
| 10661 |
+-------+
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 the server rather than being interpreted by mysql itself. See Section 23.1, "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 member.
The following example function takes a parameter, performs an operation using an SQL function, and return the result. In this case, it is unnecessary to use delimiter because the function definition contains no internal ; statement delimiters:
mysql> CREATE FUCNTION hello (s CHAR(20))
-> RETURNS CHAR(50) DETERMINISTIC
-> RETURN CONCAT ('Hello, ' , s, '!' );
mysql> SELECT hello('world');
+----------------+
| hello('world') |
+----------------+
| Hello, world! |
+----------------+
1 row in set (0.01 sec)
Parameter types and function types can be declared use any valid data type. The COLLATE attribute can be used if preceded by the CHARACTER SET attribute. 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 13.6, "Compound-Statement Syntax".
MySQL permits routines to contain DDL statements, such as CREATE and DROP. MySQL also permits stored procedures(but not stored functions) to contains 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 C.1, "Restrictions on Stored Programs".
For information about invoking stored procedures from within programs written in a language that has a MySQL interface, see Section 13.2.1, "CALL Syntax".
MySQL stores the sql_model 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 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 is 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 23.7, "Binary Logging of Stored Programs".
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 executions 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.)
Several characteristics provide information about the nature of data use by the routine. In MySQL, these characteristic are advisory only. The server does not use them to constrain what kinds of statements a routine will be 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 he EXECUTE privilege for it, as must be 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 a user value is given for the DEFINER clause, it should be a MySQL account specified as 'user_name'@'host_name', CURRENT_USER, or CURRENT_USER(). The default DEFINER value is the user who executes the CREATE PROCEDURE or CREATE FUNCTION statement. This is the same as specifying DEFINER = CURRENT_USER explicitly.
If you specify the DEFINER clause, these rules determine the valid DEFINER user values:
If you do not have the SUPER privilege, the only permitted 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 valid account name. If the account does not exist, a warning is generated.
Although it is possible to create a routine with a nonexistent DEFINER account, an error occurs at routine execution time if the SQL SECURITY value is DEFINER but the definer account does not exist.
For more information about stored routine security, see Section 23.6, ""Access Control for Stored Programs and Views".
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 6.3.12, "SQL-Based MySQL Account Activity Auditing"
Consider the following procedure, which displays a count of the number of MySQL accounts listed in the mysql.user table:
mysql> CREATE DEFINER = 'root'@'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' hash 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 hash the EXECUTE privilege for it and the SELECT privilege for the mysql.user table.
The sever 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.
For character data types, if there is a CHARACTER SET attribute 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 attributes 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 explicit CHARACTER SET and COLLATE attributes for character data parameters.
If you change the database default character set or collation, stored routines that use the database defaults must be dropped and recreated so that they use the new defaults.
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 10.1.3.3, "Database Character Set and Collation".