help with mysql select please

[georgeocrawford]

Hi,

If I have two tables, which both have a column named 'forum_id', how can I find a list of all the forum_id's which appear in table 1 but not in table 2?

eg:

table 1

forum_id forum_name
1 test
2 forum
3 george
4 hello


table 2

forum_id post_id
1 7
4 16



I want to get results of '2' and '3' from this operation.

______________________

George

 

[Moonspell]

hmm, you will need to use a join command to do this and reference the 2 fields you wish to compare.
look here look here for more info. hope this helps.

 

[georgeocrawford]

Got it - thanks a lot!

SELECT a.forum_id FROM table1 a LEFT JOIN table2 b USING (forum_id) WHERE b.forum_name is NULL

it works - does it look correct?

______________________

George

 

[Moonspell]

if it works then it looks correct. sorry, just know about this command, never used it.

 

[georgeocrawford]

thanks for the quick responses - I'm working in PHP and I've replaced 25 lines of stupid array loops with one MySQL query - NICE!

______________________

George