Update table data using table data from another table

[NEX2NUN]

I am trying to create an IF ELSE statement in MySQL to update a table using data from another table.

BEGIN
IF owners.ab = '' THEN 
SET owners.ben = ditches.min * 3 FROM owners, ditches 
WHERE owners.number = '566' AND owners.number = ditches.number
ELSE
SET owners.ben = owners.ab * ditches.acre * 3 FROM owners, ditches 
WHERE owners.number = '566' AND owners.number = ditches.number
END IF;

I get an error, of course

#1064 - You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'IF ab = '' THEN SET ben = min * 3 FROM owners, ditches WHERE owners.number =' at line 2

Sadly this explanation is past my understanding. http://dev.mysql.com/doc/refman/5.0/en/if-statement.html

Can someone please help me break this down and understand how this works??

Thank you!

[Roger_Ramjet]

First of all you need to specify 'UPDATE owners ....

Then once you have identified the query type and the table/s to operate on you can begin your IF