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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
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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
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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
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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
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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。 | 