Help with SQL UNION Query.?

SELECT * FROM xbox360 UNION ALL SELECT * FROM playstationthree WHERE GamePrice >= 1 AND GameAgeRating='15' LIMIT 10 The code is part of a products page and if the user specifies which table to browse IE without the UNISON code the query is fine at selecting the age and displaying only games that have that age but with unison applied and the table not specified it just displays everything. Any help appreciated.