Question

I have a fairly simple query I’m try to write.

If I run the following query:

SELECT parts.id, parts.type_id 
FROM parts 
WHERE parts.type_id=1 
  OR parts.type_id=2 
  OR parts.type_id=4 
ORDER BY parts.type_id;

I get all the rows I expect to be returned. Now when I try to grab the parent_unit from another table with the following query six rows suddenly drop out of the result:

SELECT parts.id, parts.type_id, sp.parent_unit 
FROM parts, serialized_parts sp 
WHERE (parts.type_id=1 OR parts.type_id=2 OR parts.type_id=4) 
  AND sp.parts_id = parts.id 
ORDER BY parts.type_id

In the past I’ve never really dealt with ORs in my queries so maybe I’m just doing it wrong. That said I’m guessing it’s just a simple mistake. Let me know if you need sample data and I’ll post some. Thanks.

Answer 1

Check the value for parts.parts_id for the 6 missing rows. You probably don’t have a corresponding value in sp.parts_id (or maybe the value for parts.parts_id is null). Note that it has to be an exact match for the join to work.

As an alternative to the OR string you can use parts.type_id IN (1,2,4). It works the same as the listed ORs but is easier to read.