How to use SQL Select statement with IF EXISTS sub query?

Question

How to select Boolean value from sub query with IF EXISTS statement (SQL Server)?

It should be something like :

SELECT    TABEL1.Id,    NewFiled = (IF EXISTS(SELECT Id FROM TABLE2 WHERE TABLE2.ID = TABEL1.ID)                   SELECT 'TRUE'                ELSE                   SELECT 'FALSE')  FROM TABEL1 

Answer 1

Use 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 

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If TABLE2.ID is Unique or a Primary Key, you could also use this:

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 

Answer 2

You can also use ISNULL and a select statement to get this result

SELECT Table1.ID, ISNULL((SELECT 'TRUE' FROM TABLE2 WHERE TABLE2.ID = TABEL1.ID),'FALSE') AS columName, etc FROM TABLE1