Question

I have 2 tables (I am using T-SQL)

Table1

ID  First_Name Last_Name Phone
--  ---------- --------- --------------
1   John       Smith     [phone] 
2   Dave       Miller    [phone]
3   Tiffany    Ovally    [phone]
4   Dan        Davis     [phone]
5   Mike       Kolis     [phone]


Table2

Iden   FirstN     LastN      PhoneN
----   ------     -----      ------
J-09   Tiffany    Ovally    [phone]
K-98   Dan        Davis     [phone]
W-03   Dave       Miller    [phone]
C-34   Mike       Kolis     [phone]

I need to check that key values from Table1 DO NOT exist in table2

I am doing the following

    IF NOT EXISTS(SELECT * FROM Table2 t2
                  WHERE t2.FirstN = (Select First_Name from Table1 where ID = @ID)
                  AND t2.LastN  = (Select Last_Name from Table1 where ID = @ID)  
                  AND t2.PhoneN = (Select Phone from Table1 where ID = @ID)        
                  )
   BEGIN
    .... 
  END

Not sure if there is a more efficient way to do this as I am doing a subquery for each field..

Thanks

Answer 1

Your query is looking for records in Table2 that do not match the record in Table1 with an ID of @ID. Using an INNER JOIN here would be better than using the multiple subqueries:

IF NOT EXISTS (SELECT *
               FROM FROM Table1 t1
               INNER JOIN Table2 t2 
                  ON  t1.First_Name = t2.FirstN
                  AND t1.Last_Name = t2.LastN
                  AND t1.Phone = t2.PhoneN
              WHERE t1.ID = @ID)
BEGIN
    ....
END