Question

为了使用MySQL动态使用游标，是否可以在存储过程的循环中声明游标？我试过并得到了一个错误：

increment: LOOP
DECLARE cur1 CURSOR FOR SELECT person_id, publication_id  FROM p_publication WHERE person_id = new_count;
DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = 1;
OPEN cur1;
REPEAT
    FETCH cur1 INTO pub_id, per_id;
IF NOT done THEN
          INSERT INTO test.t2 VALUES (pub_id, per_id);
    END IF;
SET new_count = new_count + 1;
  UNTIL done END REPEAT;

     CLOSE cur1;
IF !(new_count < old_count ) THEN LEAVE increment;
END IF;
END LOOP increment;

您的SQL语法有错误;查看与MySQL对应的手册在'DECLARE cur1 CURSOR FOR SELECT person_id附近使用正确语法的服务器版本，在第12行发布_id FROM person_has_public'

提前致谢

Answer 1

您可以通过将光标嵌套在BEGIN ... END块中来执行您想要的操作。有关详细信息，请参阅Roland Bouman's "Nesting MySQL Cursor Loops"文章。值得注意的是，他对这种技术的评论通常是不必要的，因为通常可以重写查询而不必执行嵌套游标。

如果您仍然需要将光标嵌套在循环中，您的代码应如下所示：

increment: LOOP
    block_cursor: BEGIN
        DECLARE cur1 CURSOR FOR SELECT person_id, publication_id  FROM p_publication WHERE person_id = new_count;
        DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = 1;
        OPEN cur1;
        REPEAT
            FETCH cur1 INTO pub_id, per_id;
            IF NOT done THEN
                INSERT INTO test.t2 VALUES (pub_id, per_id);
            END IF;
            SET new_count = new_count + 1;
        UNTIL done END REPEAT;
        CLOSE cur1;
        IF !(new_count < old_count ) THEN
            LEAVE increment;
        END IF;
    END block_cursor;
END LOOP increment;

在存储过程的循环中使用Cursor

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