Dumb question- where do I find my user table?
In your database. Your validation query for example would be as follows.
Code:
SELECT `id` FROM `#__users` WHERE `username` = '[value]'
Then depending on whether you want to match empty results or non-empty results will determine how it'd validate. For example in your case you'd set "Validate On" to "Successful Results".
I just found out that the validation should be shown to the moderator only (not the registrant). We don't want the registrant to know if their field matches anyone in our database. But we do want the moderator to be able to see. Because if it's not a match, it could be spelling mistake etc. that only a live person will be able to confirm.
If the field is only accessible to moderators then only they will see the validation. Otherwise yes all registered users using the field would see the validation.
Is this possible or something custom I would have to pay you guys to set up?
To have the validation only function or moderators would require custom coding/editing of the CB Query Field plugin it self, which we do not provide here. As for setting up the query to do the validation yes that can be provided as Nick explained above.