Question

I have the following table structure:

table: user
user_id | join_date
    101 | '2012-4-13'
    102 |  '2012-6-4'
    103 |        NULL
    104 |        NULL

table: job
job_id | user_id
    20 |      101
    21 |      103

I want to return a single result set of user records that contains the following:

1. The results of all users that have a match in the job table.
2. The results of all users where the join_date is null, AND do not have a record in the job table.

Here is the result set of user_id’s I would like to see:

user_id
    101 <-- has a job
    103 <-- has a job
    104 <-- never joined, AND also does not have a job

Do I need to do this using Common Table Expressions or can I do this in a subquery?

Please note I’ve left out actual details for the sake of brevity. This is not a simple case of an inner join.

Here are each of my queries running separately:

THIS IS THE QUERY THAT RETURNS THE PROPER RESULT FOR #1

SELECT DISTINCT u.*   
FROM [user] u, job uj
WHERE u.user_id = uj.user_id

THIS IS THE QUERY THAT RETURNS THE PROPER RESULT FOR #2

SELECT DISTINCT u.*   
FROM [user] u  
FULL JOIN job uj ON u.user_id = uj.user_id   
WHERE u.join_date IS NULL AND uj.user_id IS NULL 

Answer 1

This should do it:

select u.user_id from [user] u
left join job j on u.user_id = j.user_id
where j.job_id is not null or (j.job_id is null and u.join_date is null)

Edit:
This is logically the same and “simpler” but the first way “reads” like the problem statement:

select u.user_id from [user] u
left join job j on u.user_id = j.user_id
where j.job_id is not null or  u.join_date is null