Question

I’m trying to create a query that includes records from tables on the following condition:

Includes:

1. The user has a record in the job table.
2. The user has a NULL join_date OR a record in the job table

Excludes

1. The user has no record in the job table AND a NOT NULL join_date

Here’s my schema:

user --> user_id, join_date
job  --> job_id, user_id

user rows
user_id: 1, join_date: 1/24/13
user_id: 2, join_date: 1/24/13
user_id: 3, join_date: NULL
user_id: 4, join_date: NULL

job rows
job_id: 101, user_id: 1
job_id: 102, user_id: 3

I want to write a query that returns users #1, #3, and #4. I have the following query which does not return user #4:

SELECT DISTINCT u.[user_id], u.join_date, uj.job_id
FROM [user] u  
LEFT JOIN job uj ON (u.user_id = uj.user_id OR u.join_date is null)              
WHERE uj.user_id = u.user_id

Answer 1

I think this is best expressed using in in the where clause:

select *
from user u
where u.join_date is null or
      u.user_id in (select user_id from job)

If you want job information too, you can join in the job information as:

select u.*, j.job_id
from user u left outer join
     job j
     on u.user_id = j.user_id
where u.join_date is null or j.user_id is not null

This will return multiple rows per user, one for each job. You only need the distinct if a user can be listed multiple times for a single job.

Or, if you prefer:

select *
from user u
where not (u.join_date is not null and
           u.user_id not in (select user_id from job)
          )

This goes by your exclude logic.

By the way, in and not in are really just special cases of outer joins.