IN子句中不存在列,但SQL运行

我有一个使用IN子句的查询.这是一个简化版本：

SELECT *
  FROM table A
  JOIN table B
    ON A.ID = B.ID
 WHERE B.AnotherColumn IN (SELECT Column FROM tableC WHERE ID = 1)

tableC没有Column列,但查询执行得很好而没有错误消息.有人可以解释为什么吗

解决方法

例如：

CREATE TABLE #test_main (colA integer) 
CREATE TABLE #test_sub (colB integer)

-- Works,because colA is available to the sub-query from the outer query. However,-- it's probably not what you intended to do:
SELECT * FROM #test_main WHERE colA IN (SELECT colA FROM #test_sub)

-- Doesn't work,because colC is nowhere in either query
SELECT * FROM #test_main WHERE colA IN (SELECT colC FROM #test_sub)

正如Damien所观察到的,保护自己免受这种不太明显的“陷阱”的最安全的方法是养成在子查询中限定列名的习惯：

-- Doesn't work,because colA is not in table #test_sub,so at least you get
-- notified that what you were trying to do doesn't make sense.
SELECT * FROM #test_main WHERE colA IN (SELECT #test_sub.colA FROM #test_sub)

（编辑：青岛站长网）

【声明】本站内容均来自网络，其相关言论仅代表作者个人观点，不代表本站立场。若无意侵犯到您的权利，请及时与联系站长删除相关内容!