MySQL supports cursors inside stored programs. MySQL支持存储程序中的游标。The syntax is as in embedded SQL. 语法与嵌入式SQL中的相同。Cursors have these properties:游标具有以下属性:
Asensitive: The server may or may not make a copy of its result table敏感:服务器可以复制或不复制其结果表
Read only: Not updatable只读:不可更新
Nonscrollable: Can be traversed only in one direction and cannot skip rows不可遍历:只能在一个方向上遍历,不能跳过行
Cursor declarations must appear before handler declarations and after variable and condition declarations.游标声明必须出现在处理程序声明之前,变量和条件声明之后。
Example:例子:
CREATE PROCEDURE curdemo()
BEGIN
DECLARE done INT DEFAULT FALSE;
DECLARE a CHAR(16);
DECLARE b, c INT;
DECLARE cur1 CURSOR FOR SELECT id,data FROM test.t1;
DECLARE cur2 CURSOR FOR SELECT i FROM test.t2;
DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = TRUE;
OPEN cur1;
OPEN cur2;
read_loop: LOOP
FETCH cur1 INTO a, b;
FETCH cur2 INTO c;
IF done THEN
LEAVE read_loop;
END IF;
IF b < c THEN
INSERT INTO test.t3 VALUES (a,b);
ELSE
INSERT INTO test.t3 VALUES (a,c);
END IF;
END LOOP;
CLOSE cur1;
CLOSE cur2;
END;