SQL语法基础之高级应用
作者：尹正杰
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一.存储过程与函数
1>.CREATE PROCEDURE 用来创建存储过程
mysql> ? CREATE PROCEDURE Name: 'CREATE PROCEDURE' Description: 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: 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 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/8.0/en/adding-functions.html. A UDF can be regarded as an external stored function. Stored functions share their namespace with UDFs. See http://dev.mysql.com/doc/refman/8.0/en/function-resolution.html, for the rules describing how the server interprets references to different kinds of functions. To invoke a stored procedure, use the CALL statement (see [HELP CALL]). 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 SET_USER_ID or 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 http://dev.mysql.com/doc/refman/8.0/en/stored-programs-logging.html. 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 http://dev.mysql.com/doc/refman/8.0/en/stored-routines-privileges.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 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, 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. Routine parameters cannot be referenced in statements prepared within the routine; see http://dev.mysql.com/doc/refman/8.0/en/stored-program-restrictions.html . 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 enables 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/8.0/en/stored-programs-defining.html. 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. 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 http://dev.mysql.com/doc/refman/8.0/en/sql-syntax-compound-statements.h tml. 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 http://dev.mysql.com/doc/refman/8.0/en/stored-program-restrictions.html . For information about invoking stored procedures from within programs written in a language that has a MySQL interface, see [HELP CALL]. 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. URL: http://dev.mysql.com/doc/refman/8.0/en/create-procedure.html mysql>