Question

我有3个表格Tag，Software和Software_Tag，它们之间的关系是多对多。

我希望将子查询拆分为两部分（因为我无法在mysql中进行一次）：

(SELECT softwares_id FROM Software_Tag GROUP BY softwares_id HAVING COUNT(*) >=2) as my

DELETE FROM Software_Tag WHERE tags_id=1 AND softwares_id IN (my)

在这里，我尝试使用名为“my”的虚拟表将其置于第二个查询中。我怎么能这样做？

现在它像检查你的sql server 一样异常。

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Answer 1

要使用临时表，您需要这样做：

DROP TABLE IF EXISTS my_tmp;
CREATE TEMPORARY TABLE my_tmp SELECT softwares_id 
    FROM Software_Tag GROUP BY softwares_id 
    HAVING COUNT(*) >=2;
DELETE FROM Software_Tag 
    WHERE tags_id=1 
        AND softwares_id IN (SELECT softwares_id FROM my_tmp);

Answer 2

你可以这样做：

DELETE FROM Software_Tag WHERE tags_id=1 AND softwares_id IN
(SELECT softwares_id FROM Software_Tag GROUP BY softwares_id HAVING COUNT(*) >=2)

这应该适用于MySQL。

编辑..试试这个

DELETE ST1
FROM Software_Tag ST1 
JOIN (SELECT softwares_id FROM Software_Tag GROUP BY softwares_id HAVING COUNT(*) >=2) ST2 on ST1.softwares_id=ST2.softwares_id
where ST1.tags_id=1

拆分子查询和虚拟表

2 个答案: