Question

I am trying to compare two tables to find rows in each table that is not in the other. Table 1 has a groupby column to create 2 sets of data within table one.

groupby     number
----------- -----------
1           1
1           2
2           1
2           2
2           4

Table 2 has only one column.

number
-----------
1
3
4

So Table 1 has the values 1,2,4 in group 2 and Table 2 has the values 1,3,4.

I expect the following result when joining for Group 2:

`Table 1 LEFT OUTER Join Table 2`
T1_Groupby  T1_Number   T2_Number
----------- ----------- -----------
2           2           NULL

`Table 2 LEFT OUTER Join Table 1`
T1_Groupby  T1_Number   T2_Number
----------- ----------- -----------
NULL        NULL        3

The only way I can get this to work is if I put a where clause for the first join:

PRINT 'Table 1 LEFT OUTER Join Table 2, with WHERE clause'
select  table1.groupby as [T1_Groupby],
        table1.number as [T1_Number],
        table2.number as [T2_Number]
from    table1
        LEFT OUTER join table2
        --******************************
        on table1.number = table2.number
        --******************************
WHERE   table1.groupby = 2
    AND table2.number IS NULL

and a filter in the ON for the second:

PRINT 'Table 2 LEFT OUTER Join Table 1, with ON clause'
select  table1.groupby as [T1_Groupby],
        table1.number as [T1_Number],
        table2.number as [T2_Number]
from    table2
        LEFT OUTER join table1
            --******************************
            on table2.number = table1.number
            AND table1.groupby = 2
            --******************************
WHERE   table1.number IS NULL

Can anyone come up with a way of not using the filter in the on clause but in the where clause?

The context of this is I have a staging area in a database and I want to identify new records and records that have been deleted. The groupby field is the equivalent of a batchid for an extract and I am comparing the latest extract in a temp table to a the batch from yesterday stored in a partioneds table, which also has all the previously extracted batches as well. Code to create table 1 and 2:

create table table1 (number int, groupby int)
create table table2 (number int)
insert into table1 (number, groupby) values (1, 1)
insert into table1 (number, groupby) values (2, 1)
insert into table1 (number, groupby) values (1, 2)
insert into table2 (number) values (1)
insert into table1 (number, groupby) values (2, 2)
insert into table2 (number) values (3)  
insert into table1 (number, groupby) values (4, 2)  
insert into table2 (number) values (4)  

EDIT:

A bit more context – depending on where I put the filter I different results. As stated above the where clause gives me the correct result in one state and the ON in the other. I am looking for a consistent way of doing this.

Where –

select  table1.groupby as [T1_Groupby],
        table1.number as [T1_Number],
        table2.number as [T2_Number]
from    table1
        LEFT OUTER join table2
            --******************************
            on table1.number = table2.number
            --******************************
WHERE   table1.groupby = 2 
    AND table2.number IS NULL

Result:

T1_Groupby  T1_Number   T2_Number
----------- ----------- -----------
2           2           NULL

On –

select  table1.groupby as [T1_Groupby],
        table1.number as [T1_Number],
        table2.number as [T2_Number]
from    table1
        LEFT OUTER join table2
            --******************************
            on table1.number = table2.number
            AND table1.groupby = 2
            --******************************
WHERE   table2.number IS NULL

Result:

T1_Groupby  T1_Number   T2_Number
----------- ----------- -----------
1           1           NULL
2           2           NULL
1           2           NULL

Where (table 2 this time) –

select  table1.groupby as [T1_Groupby],
        table1.number as [T1_Number],
        table2.number as [T2_Number]
from    table2
        LEFT OUTER join table1
            --******************************
            on table2.number = table1.number
            AND table1.groupby = 2
            --******************************
WHERE   table1.number IS NULL

Result:

T1_Groupby  T1_Number   T2_Number
----------- ----------- -----------
NULL        NULL        3

On –

select  table1.groupby as [T1_Groupby],
        table1.number as [T1_Number],
        table2.number as [T2_Number]
from    table2
        LEFT OUTER join table1
            --******************************
            on table2.number = table1.number
            --******************************
WHERE   table1.number IS NULL
    AND table1.groupby = 2

Result:

T1_Groupby  T1_Number   T2_Number
----------- ----------- -----------
(0) rows returned

Answer 1

If you filter the left outer joined table in the WHERE clause then you are in effect creating an inner join

See also this wiki page: WHERE conditions on a LEFT JOIN