Question

The following query does not fail but does not insert the unique values either.

I only want to insert unique values

DECLARE @user_id AS varchar(80) 
DECLARE @real_name as varchar(250) 

–New Unique values are “aaa” and they do not exist in the target table

SET @user_id = 'aaa'
SET @real_name = 'aaa'

INSERT INTO TargetTable
  ([user_id],real_name)
SELECT @user_id, @real_name
WHERE NOT EXISTS
  (SELECT [user_id],real_name FROM TargetTable)

Answer 1

If you’re having problem with the insert the way you doing, try a different approach like this:

-- if the count of records with that @user_id and @real_name is less or equal to 0, 
-- that means it's not in the table
IF (0 >= (SELECT COUNT(*) FROM TargetTable WHERE @user_id = [user_id] AND @real_name = [real_name]))
BEGIN
   -- then call a normal insert
   INSERT
     INTO TargetTable ([user_id], real_name )
   VALUES             (@user_id , @real_name)

END