I’m sure everyone else already knows this stuff, but since I use my blog for reference when I don’t feel like trying to look things up, I’m going to do another piece on SQL. Specifically, another piece on SQL subselects.
This time I needed to update a field, instead of deleting from a file. So the subselect was used in place of a join or something else that would just be too much work.
UPDATE targetfile SET targetfield = (select sourcefield from sourcefile where targetfile.targetfield = sourcefile.sourcefield) where checkfield = checkvalue
If you use multiple fields to perform your join, simply separate them with an and: targetfile.targetfieldone = sourcefile.sourcefieldone and targetfile.targetfieldtwo = sourcefile.sourcefieldtwo. That’s all there is to it!