I am new to MySQL and am ploughing through.
A question I am sure everyone else can answer without trying:

How do I code an SQL statement to do this (if I can?):

Select the required account

IF the account is found

IF the balance is less than $100
DO y
ELSE
DO z
ENDIF

ENDDO

And how would this interact with my website/PHP? Checking '$result' would show mw what? Or would I code 2 seperate SQL statements from my PHP script?

Hope I am not showing myself to be too ignorant here!

when you select the account from the table, you can use a CASE expression to return something if the balance is < 100, and something else if the balance is >= 100

however, if you want to do something, then this will have to be done with php

Thanks r937
just to get this right:
In my PHP script set up a query to check for the record's existence on the table
If I find it, I do the checking in the PHP script on the balance
Depending on the balance I perform the appropriate action - is that correct.

What do I do if somebody else comes along and updates the balance while I am checking it - or is this beyond ths scope of this thread?

yes, i think you have to lock the record

just what is this "appropriate action" that needs doing?