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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.
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原文地址：http://www.cnblogs.com/free-coder/p/4774736.html
