Question

I’m having a problem moving from a situation where an Outer Join works, to where it fails.

Working (pseudo code example)

SELECT a.number, a.name, b.ref, c.ref, c.firmref
FROM jobs a, teams b LEFT OUTER JOIN teamfirms c ON b.ref = c.team
WHERE a.ref = b.job

There is a many to one relationship between jobs and teams (many teams per job) that is always populated

There may or may not be firms in table c, but the query above gives me the result I would expect (approx 5000 records)

The problem comes when I want to bring in the details about the teams from a fourth table

The code I am trying is below

SELECT a.number, a.name, b.ref, c.ref, c.firmref, d.name
FROM jobs a, teams b LEFT OUTER JOIN teamfirms c ON b.ref = c.team, firms d
WHERE a.ref = b.job
AND d.ref = c.firmref

At this point the NULLS that I am trying to capture disappear and I drop approx 500 records

What am I doing wrong?

Answer 1

take a whack at this.

select a.number, a.name, b.ref, c.ref, c.firmref, d.name
from jobs a left outer join teams b on b.job = a.ref
left outer join teamfirms c on b.ref = c.team
left outer join firms d on c.firmref = d.ref
left outer join table e on a.column = e.column

or you could do

select a.number, a.name, b.ref, c.ref, c.firmref, d.name
from
jobs a, teams b, teamfirms c, firms d
where
a.ref = b.job
and b.ref = c.team
and c.firmref = d.ref

one or the other… not both.

Just to throw this in for good measure…

You use INNER JOIN to return all rows
from both tables where there is a
match. ie. in the resulting table all
the rows and colums will have values.

LEFT OUTER JOIN returns all the rows
from the first table, even if there
are no matches in the second table.

RIGHT OUTER JOIN returns all the rows
from the second table, even if there
are no matches in the first table.