mysql SQL_CALC_FOUND_ROWS problem with join

Why this query returning 0 rows?

SELE开发者_开发问答CT SQL_CALC_FOUND_ROWS a.*, b.id AS key1, b.name AS catname 
FROM #__cd_ads a
LEFT JOIN #__cd_categories b ON a.type = b.id

when removed b.id AS key1, b.name AS catname than works.