Question

I am working with a badly designed database and I ran into some problem.

I have two tables that I need to join on a ‘not unique ID’.
The software that currently works with the database sets a ‘0 value’ in the id if there is an error. This means if I try to join them a massive amount of records is joined on the 0 values.

Underneath an example of two tables and their not unique id fields i want to join them on

tbl1    tbl2
-----------       
2        2
3        6
4        5
0        3
0        4
6        0
5        0
----------

What I want to achieve is this

tbl1    tbl2
-----------         
2        2
3        3
4        4
0        * (no join)
0        * (no join)
6        6
5        5
----------

In other words, I don’t want the ‘0 values’ from tbl1 to join with all other ‘0 values’ from tbl2. I still want to have the record tbl1 without a join though.

Is this possible in 1 query?

extra information: SQL SERVER 2005 and there is no option to make the ID’s unique.

Answer 1

This should do the trick

SELECT * FROM tbl1
LEFT JOIN tbl2 ON tbl1.value = tbl2.value and tbl2.value <> 0

this will give null values on the two that you put as *