MySQL存储过程之流程控制

1. 条件分支IF-THEN-ELSE-END IF

 1 CREATE PROCEDURE p12 (IN parameter1 INT)
 2 BEGIN
 3     DECLARE variable1 INT;
 4     SET variable1 = parameter1 + 1;
 5     IF variable1 = 0 THEN
 6         INSERT INTO t VALUES (17);
 7     END IF;
 8     IF parameter1 = 0 THEN
 9         UPDATE t SET s1 = s1 + 1;
10     ELSE
11         UPDATE t SET s1 = s1 + 2;
12     END IF;
13 END; //

2. CASE指令

 1 CREATE PROCEDURE p13 (IN parameter1 INT)
 2 BEGIN
 3     DECLARE variable1 INT;
 4     SET variable1 = parameter1 + 1;
 5     CASE variable1
 6     WHEN 0 THEN
 7         INSERT INTO t VALUES (17);
 8     WHEN 1 THEN
 9         INSERT INTO t VALUES (18);
10     ELSE
11         INSERT INTO t VALUES (19);
12     END CASE;
13 END; // 

3. Loops循环

　　1) WHILE...END WHILE

1 CREATE PROCEDURE p14 ()
2 BEGIN  
3     DECLARE v INT;    
4     SET v = 0;  
5     WHILE v < 5 DO  
6         INSERT INTO t VALUES (v);
7         SET v = v + 1;
8     END WHILE;
9 END; // 

　　2) REPEAT...END REPEAT

 1 CREATE PROCEDURE p15 ()
 2 BEGIN
 3     DECLARE v INT;
 4     SET v = 0;
 5     REPEAT
 6         INSERT INTO t VALUES (v);
 7         SET v = v + 1;
 8         UNTIL v >= 5    /* 此处引号可省,也可不写 */
 9     END REPEAT;
10 END; //

　　3) LOOP...END LOOP

 1 CREATE PROCEDURE p16 ()
 2 BEGIN
 3     DECLARE v INT;
 4     SET v = 0;
 5     loop_label: LOOP
 6         INSERT INTO t VALUES (v);
 7         SET v = v + 1;
 8         IF v >= 5 THEN
 9             LEAVE loop_label;
10         END IF;
11     END LOOP;
12 END; //

　　a. LOOP循环与WHILE相似,不需要初始条件,同时又与REPEAT循环一样没有结束条件.在循环开始的loop_label:用于标识该循环,而IF结构里的LEAVE loop_label表示离开循环.

　　b. Labels标号可用在BEGIN,WHILE,REPEAT或者LOOP之前,语句标号只能在合法的语句前使用,所以,LEAVE <标号名称>意味着离开与该标号对应的语句或复合语句:

 1 CREATE PROCEDURE p17 ()
 2 label_1: BEGIN
 3     label_2: WHILE 0 = 1 DO
 4         LEAVE label_2;
 5     END  WHILE;
 6     label_3: REPEAT
 7         LEAVE label_3;
 8         UNTIL 0 =0
 9     END REPEAT;
10     label_4: LOOP
11         LEAVE label_4;
12     END LOOP;
13 END; //     

　　c. End Labels标号结束符,可以用在在由标号定义的语句结束之后,无功能性作用,只起到说明的作用:

 1 CREATE PROCEDURE p18 ()
 2 label_1: BEGIN
 3     label_2: WHILE 0 = 1 DO
 4         LEAVE label_2;
 5     END  WHILE label_2;
 6     label_3: REPEAT
 7         LEAVE label_3;
 8         UNTIL 0 =0
 9     END REPEAT label_3
10     label_4: LOOP
11         LEAVE label_4;
12     END LOOP  label_4
13 END label_1  //    

　　d. LEAVE and Labels:LEAVE语句使程序跳出复杂的复合语句:

 1 CREATE PROCEDURE p19 (parameter1 CHAR)
 2 label_1: BEGIN
 3     label_2: BEGIN
 4         label_3: BEGIN
 5             IF parameter1 IS NOT NULL THEN
 6                 IF parameter1 = ‘a‘ THEN
 7                     LEAVE label_1;
 8                 ELSE
 9                     BEGIN
10                         IF parameter1 = ‘b‘ THEN
11                             LEAVE label_2;
12                         ELSE
13                             LEAVE label_3;
14                         END IF;
15                     END;
16                 END IF;
17             END IF;
18         END;
19     END;
20 END;//

　　e. ITERATE迭代:如果目标是迭代语句,就必须用到LEAVE语句,ITERATE和LEAVE语句一样可以在循环内部使用,类似c语言的continue:

 1 CREATE PROCEDURE p20 ()
 2 BEGIN
 3     DECLARE v INT;
 4     SET v = 0;
 5     loop_label: LOOP
 6         IF v = 3 THEN
 7             SET v = v + 1;
 8             ITERATE loop_label;
 9         END IF;
10         INSERT INTO t VALUES (v);
11         SET v = v + 1;
12         IF v >= 5 THEN
13             LEAVE loop_label;
14         END IF;
15     END LOOP;
16 END; // 

　　4) GOTO

1 CREATE PROCEDURE p...
2 BEGIN
3     ...
4     LABEL label_name;
5     ...
6     GOTO label_name;
7     ...
8 END;

　　虽然不是标准的SQL语句,MySQL的存储过程中仍然可以使用GOTO语句,此处标号的使用与前面不同,出于和其他DBMS兼容,此处用法慢慢被淘汰.