如果表a和表b中存在值，则向表a添加列

Question

我知道如何检查两个表中是否存在值，但是如何添加列表明它找到了什么

SELECT NAME, ID FROM TABLE_A TA
WHERE EXISTS (SELECT 1 FROM TABLE_B TB
              WHERE TA.ID = TB.ID)

结果

NAME  ID
1    123
2    234
3    345

我想要什么

NAME  ID    Exists
1    123     Y
2    234     N
3    345     N

Answer 1

可能是这个作品

SELECT NAME, ID,case when 
    (select count(1) from TABLE_B where ID = TA.ID) = 0 then 'N'
else 'Y'
end as 'Exists' FROM TABLE_A TA
WHERE EXISTS (SELECT 1 FROM TABLE_B TB
              WHERE TA.ID = TB.ID)

Answer 2

您可以在案例陈述中使用存在标准：

SELECT NAME, ID, CASE WHEN EXISTS (SELECT 1 FROM TABLE_B TB
              WHERE TA.ID = TB.ID) THEN 'Y' else 'N' end [Exists] FROM TABLE_A TA

Answer 3

SELECT TA.NAME, TA.ID,CASE WHEN TB.ID IS NULL THEN 'N' ELSE 'Y' END AS Y_N
FROM 
(select NAME, ID FROM TABLE_A)TA LEFT JOIN
(SELECT ID FROM TABLE_B)TB ON 
          TA.ID = TB.ID

Answer 4

SELECT NAME, COALESCE(TA.ID, TB.ID), 
CASE WHEN TB.Id IS NULL OR TA.ID IS NULL THEN 'N' else 'Y' end [Exists] 
FROM TABLE_A TA
FULL OUTER JOIN  TABLE_B TB
 ON TA.ID = TB.ID

这将为您提供两个表的结果，因此如果B中存在ID但不存在A，您也将获得resutls。

如果您只需要Tablea中值或不在B

中的值的结果

SELECT NAME, TA.ID, CASE WHEN TB.Id IS NULL  THEN 'N' else 'Y' end [Exists] 
FROM TABLE_A TA
LEFT OUTER JOIN  TABLE_B TB
 ON TA.ID = TB.ID