SQL Help required

[CaronaBlog]

this is my current MySQL script for my game:

SELECT * FROM `research` WHERE `id` NOT IN (SELECT `research_id` FROM `research_done` WHERE `cid` = 1) AND `gold` < 999 AND `level` <= 1 AND `required` IN (SELECT `research_id` FROM `research_done` WHERE `cid` = 1)

but i want the last IN to only work when `required` is not NULL

any suggestions?

[JGadrow]

Wouldn't that simply be:

SELECT * FROM `research` WHERE `id` NOT IN (SELECT `research_id` FROM `research_done` WHERE `cid` = 1) AND `gold` < 999 AND `level` <= 1 AND (`required` = NULL || `required` IN (SELECT `research_id` FROM `research_done` WHERE `cid` = 1));

Or you can change to `required` != NULL, depending upon what you want to achieve.