Question

Suppose two tables test1 and test2 on which I select values from both tables using a join.

My requirement is this: when I join the two tables, if test1 has data in it but no corresponding data is found in test2, then the query should throw exception.

How can this be accomplished?

Answer 1

You need RAISEERROR

Do left join and select where the right side is null. If the count > 0 throw the exception.

DECLARE @count INT

SELECT 
   @count = COUNT(*)
FROM
  test1 t1
LEFT JOIN test2 t2 
  ON t1.t1_join_col = t2.t2_join_col
WHERE 
  t2.t2_join_col IS NULL -- find where we have test1 data but not test2 data

-- Check if I need to raise an error
IF @count <> 0 
    RAISERROR (N'<<%7.3s>>', -- Message text.
           10, -- Severity,
           1, -- State,
           N'abcde'); -- First argument supplies the string.
    -- The message text returned is: <<    abc>>.

if you need to return the results where don’t match, then add the following ELSE

ELSE

SELECT 
  ... cols you want
FROM
  test1 t1
LEFT JOIN test2 t2 
  ON t1.t1_join_col = t2.t2_join_col

You could always, put the results into a temp table and count off that, and then return off that too if you prefer to do the query only once.