如何在 IF EXISTS 子查询中使用 SQL Select 语句？
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How to use SQL Select statement with IF EXISTS sub query?
提问by Nalaka526
How to select Boolean value from sub query with IF EXISTS statement (SQL Server)?
如何使用 IF EXISTS 语句 (SQL Server) 从子查询中选择布尔值？
It should be something like :
它应该是这样的：
SELECT
TABEL1.Id,
NewFiled = (IF EXISTS(SELECT Id FROM TABLE2 WHERE TABLE2.ID = TABEL1.ID)
SELECT 'TRUE'
ELSE
SELECT 'FALSE')
FROM TABEL1
回答by ypercube??
Use CASE:
使用CASE：
SELECT
TABEL1.Id,
CASE WHEN EXISTS (SELECT Id FROM TABLE2 WHERE TABLE2.ID = TABLE1.ID)
THEN 'TRUE'
ELSE 'FALSE'
END AS NewFiled
FROM TABLE1
If TABLE2.IDis Unique or a Primary Key, you could also use this:
如果TABLE2.ID是唯一键或主键，您也可以使用：
SELECT
TABEL1.Id,
CASE WHEN TABLE2.ID IS NOT NULL
THEN 'TRUE'
ELSE 'FALSE'
END AS NewFiled
FROM TABLE1
LEFT JOIN Table2
ON TABLE2.ID = TABLE1.ID
回答by Purplegoldfish
You can also use ISNULL and a select statement to get this result
您还可以使用 ISNULL 和 select 语句来获得此结果
SELECT
Table1.ID,
ISNULL((SELECT 'TRUE' FROM TABLE2 WHERE TABLE2.ID = TABEL1.ID),'FALSE') AS columName,
etc
FROM TABLE1
回答by onedaywhen
SELECT Id, 'TRUE' AS NewFiled FROM TABEL1
INTERSECT
SELECT Id, 'TRUE' AS NewFiled FROM TABEL2
UNION
SELECT Id, 'FALSE' AS NewFiled FROM TABEL1
EXCEPT
SELECT Id, 'FALSE' AS NewFiled FROM TABEL2;
回答by satnhak
Use a CASEstatement and do it like this:
使用一个CASE语句并这样做：
SELECT
T1.Id [Id]
,CASE WHEN T2.Id IS NOT NULL THEN 'TRUE' ELSE 'FALSE' END [Has Foreign Key in T2]
FROM
TABLE1 [T1]
LEFT OUTER JOIN
TABLE2 [T2]
ON
T2.Id = T1.Id
