SQL Server - select records from one table which are not in a subset of another table

Question

I am trying to prepare a query to insert new entries in a daily report into a separate table in a SQL Server database.

I have two tables as follows:

Table 1

id   style_code   location_code
-------------------------------
 1   abcd         IST
 2   abcd         DEL
 3   wxyz         DEL

Table 2

id    style_code   location_code
--------------------------------
 1    abcd         IST
 2    wxyz         IST
 3    abcd         DEL
 4    wxyz         DEL

I want to select all the rows in Table 2 where the combination of 'style_code' and 'location_id' DO NOT exist in Table 1. In this particular example, that would mean returning row 2 from Table 2 as 'wxyx & IST' do not exist in Table 1. (There is no relationship between the id columns. Table 2 is a temporary table)

I have been trying to put a join into a Select query with NOT IN, but I cannot seem to get the query to work correctly.

SELECT *
FROM [Table 2]
WHERE style_code NOT IN (SELECT style_code
                         FROM [Table 1] 
                         INNER JOIN [Table 2] ON [Table 2].location_code = [Table 1].location_code);

I have a beginners understanding of SQL coding, but am no expert, and would appreciate any guidance.

Answer 1

You can use NOT EXISTS and a correlated subquery.

SELECT *
       FROM [Table 2] t2
       WHERE NOT EXISTS (SELECT *
                                FROM [Table 1] t1
                                WHERE t1.style_code = t2.style_code
                                      AND t1.location_code = t2.location_code);

Answer 2

You can use NOT EXISTS :

SELECT *
FROM [Table 2]
WHERE NOT EXISTS (SELECT1
                  FROM [Table 1] 
                  WHERE [Table 2].location_code = [Table 1].location_code AND
                        [Table 2].style_code = [Table 1].style_code
                 );

Some databases -- increasingly more and more of them -- do support multiple columns with IN and NOT IN . However, SQL Server is not among them.

In addition, I strongly recommend using NOT EXISTS instead of NOT IN when using a subquery. NOT IN does not behave intuitively if any of the values returned by the subquery are NULL . In that case, NOT IN filters out all rows and the result set is empty.

Answer 3

Alternate way - You can achieve this using a LEFT OUTER JOIN . This SQL may give you better performance than NOT EXISTS or NOT IN clauses.

select t2.id, t2.style_code, t2.location_code 
from table_2 t2 left outer join table_1 t1 
on t2.style_code = t1.style_code
and t2.location_code = t1.location_code
where t1.style_code is null;