10.1.6  流程控制的使用

        （1）IF語句的使用。

DROP PROCEDURE IF EXISTS testIf;
DELIMITER //
CREATE PROCEDURE testIf(OUT result VARCHAR(255))
BEGIN
     DECLARE val VARCHAR(255);
     SET val = 'a';
     IF val IS NULL
        THEN SET result = 'IS NULL';
        ELSE SET result = 'IS NOT NULL';
     END IF;
END //
DELIMITER ;

CALL testIf(@result);
SELECT @result;
 

        （2）CASE語句

DROP PROCEDURE IF EXISTS testCase;
DELIMITER //
CREATE PROCEDURE testCase(OUT result VARCHAR(255))
BEGIN
     DECLARE val VARCHAR(255);
     SET val = 'a';
     CASE val IS NULL
         WHEN 1 THEN SET result = 'val is true';
         WHEN 0 THEN SET result = 'val is false';
         ELSE SELECT 'else';
     END CASE;
END //
DELIMITER ;

CALL testCase(@result);
SELECT @result;
 

        （3）LOOP

        LOOP用於重複執行SQL。LEAVE 用於退出迴圈。

DROP PROCEDURE IF EXISTS testLoop;
DELIMITER //
CREATE PROCEDURE testLoop(OUT result VARCHAR(255))
BEGIN
     DECLARE id INT DEFAULT 0;
     add_loop:LOOP
	   SET id = id + 1;
	   IF id>10 THEN LEAVE add_loop; -- 可在此處修改成批量插入
	   END IF;
     SET result = id;
     END LOOP add_loop;
END //
DELIMITER ;

CALL testLoop(@result);
SELECT @result;
 

        下面是一個批量插入的例子

DROP TABLE IF EXISTS t_student;
 
CREATE TABLE t_student
(
    id INT(11) PRIMARY KEY AUTO_INCREMENT,
  name VARCHAR(255) NOT NULL,
  age  INT(11) NOT NULL
);

DROP PROCEDURE IF EXISTS testLoop;
DELIMITER //
CREATE PROCEDURE testLoop(IN columnCount INT(11))
BEGIN
     DECLARE id INT DEFAULT 0;
     add_loop:LOOP
	SET id = id + 1;
	IF id>columnCount THEN LEAVE add_loop;
	END IF;
       INSERT INTO t_student(id,name,age) VALUES(id,'dayu',22);
     END LOOP add_loop;
END //
DELIMITER ;

CALL testLoop(15);

        （4）WHILE

DROP PROCEDURE IF EXISTS testWhile;
DELIMITER //

CREATE PROCEDURE testWhile(IN myCount INT(11),OUT result INT(11))
BEGIN
   DECLARE i INT DEFAULT 0 ; 
   WHILE i < myCount DO
       SET i = i + 1 ; 
   END WHILE;
   SET result = i;
END //
CALL testWhile(10,@result);
SELECT @result AS 迴圈次數;