删除基于多行选择

Question

我试图做一个触发器，它会从一个基于表中选择删除另一个表中的行

表operatorpositions 列operator，line，pos

表positiontags 色谱柱line,position,tag

表operatortags co lumns operator，tag

我的触发看起来像这样

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; 

问题是可以有多个标签为一个位置，这样子查询将返回多行。我如何需要改变它，以便它可以使用多个标签？

Answer 1

如果我明白你想删除所有标签。
所以尽量用IN

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; 

改变从=到IN运营商子查询之前更换你=应于子返回多行

Answer 3

更有效的方式来做到这一点是利用工作一个加入 -

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;