Each stored program contains a body that consists of an SQL
statement. This statement may be a compound statement made up of
several statements separated by semicolon (;
)
characters. For example, the following stored procedure has a body
made up of a BEGIN ...
END
block that contains a
SET
statement and a
REPEAT
loop that itself contains another
SET
statement:
CREATE PROCEDURE dorepeat(p1 INT) BEGIN SET @x = 0; REPEAT SET @x = @x + 1; UNTIL @x > p1 END REPEAT; END;
If you use the mysql client program to define a stored program that contains the semicolon characters within its definition, a problem arises. By default, mysql itself recognizes semicolon as a statement delimiter, so you must redefine the delimiter temporarily to cause mysql to pass the entire stored program definition to the server.
To redefine the mysql delimiter, use the
delimiter
command. The following example shows
how to do this for the dorepeat()
procedure
just shown. The delimiter is changed to //
to
enable the entire definition to be passed to the server as a
single statement, and then restored to ;
before
invoking the procedure. This enables the ;
delimiter used in the procedure body to be passed through to the
server rather than being interpreted by mysql
itself.
mysql>delimiter //
mysql>CREATE PROCEDURE dorepeat(p1 INT)
->BEGIN
->SET @x = 0;
->REPEAT SET @x = @x + 1; UNTIL @x > p1 END REPEAT;
->END
->//
Query OK, 0 rows affected (0.00 sec) mysql>delimiter ;
mysql>CALL dorepeat(1000);
Query OK, 0 rows affected (0.00 sec) mysql>SELECT @x;
+------+ | @x | +------+ | 1001 | +------+ 1 row in set (0.00 sec)
You can redefine the delimiter to a string other than
//
, and the delimiter can consist of a single
character or multiple characters. You should avoid the use of the
backslash (“\
”) character because
that is the escape character for MySQL.
The following is an example of a function that 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)