SQL中使用循环结构

解答 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
---------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;

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;