SQL：獲取關於 'IN' 運算可能的值，從兩個不同的表

Question

我有3個表有以下模式：

表1列：ID MSGNUM消息 表2列：ID MSGNUM SYSTEMID 表3列：ID MSGNUM IncidentNum

我想從表2和表3。

從表2選擇的一個值的範圍內的表1 MSGNUM所有項目，使用以下SQL獲得用於MSGNUM可能的值：

SELECT Table2.MsgNum from Table2 WHERE SystemId = 'Sys-0001' 

，並從表3，

SELECT Table3.MsgNum from Table3 WHERE IncidentNumber = 'Incident-0001' 

現在，我就喜歡用從以前的2條SELECT語句獲得MSGNUM值的組合，以獲得在表1中相應的行如下：

SELECT * from Table1 where MsgNum IN (SELECT Table2.MsgNum from Table2 WHERE SystemId = 'Sys-0001' OR SELECT Table3.MsgNum from Table3 WHERE IncidentNumber = 'Incident-0001') 

但是，此SQL使用Interactive SQL失敗。我究竟做錯了什麼？

Answer 1

你的意思是工會嗎？

SELECT * 
from Table1 
where MsgNum IN 
( 
SELECT Table2.MsgNum from Table2 WHERE SystemId = 'Sys-0001' 
UNION 
SELECT Table3.MsgNum from Table3 WHERE IncidentNumber = 'Incident-0001' 
) 

Answer 2

使用UNION命令將兩個查詢一起

SELECT * from Table1 where MsgNum IN (
SELECT Table2.MsgNum from Table2 WHERE SystemId = 'Sys-0001' 
    UNION 
    SELECT Table3.MsgNum from Table3 WHERE IncidentNumber = 'Incident-0001') 
) 

Answer 3

你爲什麼不使用exists代替

SELECT * from Table1 t1 
where EXISTS (SELECT t2.MsgNum from Table2 t2 
WHERE t2.SystemId = 'Sys-0001' AND t2.MsgNum = t1.MsgNum) 
OR EXISTS (SELECT t3.MsgNum from Table3 t3 
WHERE t3.IncidentNumber = 'Incident-0001' AND t3.MsgNum = t1.MsgNum)