mysql联表查询 使用别名进行where比较

select gd_reg.*, tbl_menu_sub.menunames as gdnames FROM 
(SELECT substring_index(gd_reg.gdname,',', -1) as gdnamedemo, gd_reg.* FROM gd_reg) 
gd_reg,tbl_menu_sub WHERE gdnamedemo = tbl_menu_sub.id
ORDER BY id DESC LIMIT 10 offset 00