will this join work?

[Anon]

Trying to use the following query to get a list of usernames in table1 that are NOT in table13....this just ties up resources and gets no results, any ideas would be appreciated.

SELECT Username FROM table1, table13 WHERE table1.username != table13.username;

Thanks!

Kev

[Anon]

try
select usrname from tbl1 minus select usrname from tbl2

in ur code, wat u've done is a 'cartesian product'...quick explaination

tbl1 = [a, b, c]
tbl2 = [c, d]
the db will do
is a == c
is a == d
is b == c
is b == d
is c == c
is c == d

this will always result in tbl1, since at least one of the conditions for each element will be true.

hope this helps 😮)
Tiang

[[deleted]]

You may want to read some more about JOINs.

This query will try to match records based on the fact that something is different from something else. If you have one record where something=somethingelse, then all other records must match on
something!=somethingelse
So for every record on table1, you will get all records from table2, except those where something=somethingelse.

What you want is to always match the records on something=somethingelse, and only get those records where such a match could not be made.

SELECT *
FROM table1 LEFT JOIN table2 ON something=somethingelse
WHERE somethingelse IS NULL

[Anon]

Isn't a LEFT OUTER JOIN the solution to this?

[[deleted]]

Well, that would give the same result yes.