循环操作是数据库中经常遇到的操作，那么如何在SQL中使用循环结构呢？下文将带您寻找答案。

FOR,LOOP,WHILE,REPEAT是UDB/400的一种内部循环控制，用于遍历表中符合条件的每一行记录。
例如：
目的：更新employee库，把所有北京籍员工的工资提高10%

例一：使用FOR循环
--------------------------------------------
CREATE PROCEDURE QGPL/TEST_FOR
LANGUAGE SQL
BEGIN
FOR each_record AS
---cur01 CURSOR FOR
------SELECT * FROM code,salary,city from employee where city="Beijing"
---------DO
------------UPDATE employee
------------SET salary=salary * 1.1
------------WHERE CURRENT OF cur01;
ENDFOR;
END;

例二：使用LOOP循环
----------------------------------------
CREATE PROCEDURE QGPL/TEST_LOOP
LANGUAGE SQL
BEGIN
DECLARE code_v char(10);
DECLARE salary_v integer;
DECLARE city_v char(20);

DECLARE C1 CURSOR FOR
---SELECT code,salary,city FROM employee WHERE city="Beijing";
OPEN C1;
loop_label:
LOOP
- FETCH C1 INTO code_v,salary_v,city_v;
--IF SQLCODE=0 THEN
------SET salary_v=salary_v*1.1;
------UPDATE employee SET salary=salary_v#p#
---------WHERE CURRENT OF C1;
--ELSE
------LEAVE loop_label;
--END IF;
END LOOP loop_label;
CLOSE C1;
END;

例三：使用WHILE循环
---------------------------------------
CREATE PROCEDURE QGPL/TEST_WHILE
LANGUAGE SQL
BEGIN
DECLARE code_v char(10);
DECLARE salary_v integer;
DECLARE city_v char(20);
DECLARE at_end integer;

DECLARE C1 CURSOR FOR
---SELECT code,salary,city FROM employee WHERE city="Beijing";
OPEN C1;

SET at_end=0;
WHILE at_end = 0 DO
--FETCH C1 INTO code_v,salary_v,city_v;
--IF SQLCODE=0 THEN
------SET salary_v=salary_v*1.1;
------UPDATE employee SET salary=salary_v
---------WHERE CURRENT OF C1;
--ELSE
------SET at_end=1;
--END IF;
END WHILE;
CLOSE C1;
END;#p#

例四：使用REPEAT循环
------------------------------------------------
CREATE PROCEDURE QGPL/TEST_REPEAT
LANGUAGE SQL
BEGIN
DECLARE code_v char(10);
DECLARE salary_v integer;
DECLARE city_v char(20);

DECLARE C1 CURSOR FOR
---SELECT code,salary,city FROM employee WHERE city="Beijing";
OPEN C1;

repeat_label:
REPEAT
--FETCH C1 INTO code_v,salary_v,city_v;
--IF SQLCODE=0 THEN
------SET salary_v=salary_v*1.1;
------UPDATE employee SET salary=salary_v
---------WHERE CURRENT OF C1;
--END IF;
--UNTIL SQLCODE<>0;
END REPEAT repeat_loop;
CLOSE C1;
END;

总结：四种循环结构实现的功能基本相同，用户可以根据自己的习惯选择使用。

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