Syntax:
IF(expr1,expr2,expr3)

If expr1 is TRUE (expr1 <> 0 and expr1 <> NULL) then IF() returns
expr2; otherwise it returns expr3. IF() returns a numeric or string
value, depending on the context in which it is used.

URL: http://dev.mysql.com/doc/refman/5.1/en/control-flow-functions.html

