SQL Joint query for unmatched rows in left table

Question

I got two tables,sfuser and membership

sfuser got 139 and membership table got 50

I need the query to pick who are not a member of any project which means 89 members

Here is my query

select sfuser.id,sfuser.username,sfuser.email from sfuser INNER JOIN projectmembership ON sfuser.id = projectmembership.member_id ;

But am getting the 50 users who are members i want the other way around

Kindly throw some light

Best Regards Sathish

Answer 1

select 
sfuser.id,
sfuser.username,
sfuser.email 
from sfuser 
LEFT JOIN projectmembership ON sfuser.id = projectmembership.member_id
WHERE 
projectmembership.member_id is NULL

It should return all users that isn't in projectmembership table.

Answer 2

INNER JOIN will only produce rows that matches both tables.. You can do a left join and filter out the blank records. something like:

SELECT sfuser.id,
sfuser.username,
sfuser.email
FROM sfuser LEFT JOIN projectmembership ON sfuser.id = projectmembership.member_id
WHERE (projectmembership.member_id is null);

Answer 3

An inner join will return all rows where the values the join is done on are shared between the two tables. (See this chart )

What you are looking for is a left join, that is, all rows in the left table that have no match in the right.

select sfuser.id,
  sfuser.username,
  sfuser.email 
from sfuser 
LEFT JOIN projectmembership 
  ON sfuser.id = projectmembership.member_id

Answer 4

If sfuser records can have multiple occurrences in the project membership table then forget the outer join -- NOT EXISTS is what you want:

select sid,
       username,
       email
from   sfuser
where  not exists (
         select null
         from   projectmembership
         where  sfuser.id = projectmembership.member_id);