Question

我正在尝试创建一个触发器，它将根据另一个表中的select

从一个表中删除行

表格operatorpositions 列operator，line，pos

表格positiontags 列line，position，tag

表格operatortags 列operator，tag

我的触发器看起来像这样

CREATE TRIGGER removeOperatorPosition AFTER DELETE ON operatorpositions
    FOR EACH ROW
    BEGIN
        DELETE FROM operatortags WHERE gen = NEW.operator 
            AND tag = (SELECT tag FROM positiontags WHERE position = NEW.pos AND line = NEW.line);            
    END;

问题是一个位置可能有多个标记，因此子查询将返回多行。我该如何更改它以便它可以使用多个标签？

Answer 1

如果我理解你，你想要删除所有标签所以尝试在子查询之前用IN

替换你的=

CREATE TRIGGER removeOperatorPosition AFTER DELETE ON operatorpositions
    FOR EACH ROW
    BEGIN
        DELETE FROM operatortags WHERE gen = NEW.operator 
            AND tag IN (SELECT tag FROM positiontags WHERE position = NEW.pos AND line = NEW.line);            
    END;

Answer 2

CREATE TRIGGER removeoperatorposition AFTER DELETE
ON operatorpositions
FOR EACH ROW
BEGIN
  DELETE FROM operatortags
  WHERE  gen = new.operator
         AND tag IN (SELECT tag
                     FROM   positiontags
                     WHERE  position = new.pos
                            AND line = new.line);
END;

从=更改为IN运算符应该可以处理返回多行的子查询

Answer 3

更有效的方法是使用连接 -

CREATE TRIGGER removeOperatorPosition AFTER DELETE ON operatorpositions
    FOR EACH ROW
    BEGIN
        DELETE ot
        FROM operatortags ot
        INNER JOIN positiontags pt
            ON ot.tag = pt.tag
        WHERE ot.gen = OLD.operator 
        AND pt.position = OLD.pos
        AND pt.line = OLD.line;            
    END;

根据select删除多行

3 个答案: