I am not sure what MySQL likes, but your calculation returns date in y-m-d format. For yyyy-mm-dd, try:
Year ( YourDate ) & SerialIncrement ( "-00" ; Month ( YourDate ) ) & SerialIncrement ( "-00" ; Day ( YourDate ) )
(This is assuming all your dates are later than year 999.)
Thanks for the solution. Your calculation worked.
My calculation also worked. The problem was that I didn't enclose the calculation in ' calc ' and so filemaker treated it as a number rather than as text.