数据库中有两张表,users表中有三个字段(user__id,user__name,create__at),orders表中有三个字段(order__id,user__id,amount)(1)查询users表中存在而orders表中不存在的user__id()
A.selectusers.user_idfromusersleftjoinordersonusers.user_id=orders.user_id
B.selectusers.user_idfromusersrightjoinordersonusers.user_id=orders.user_id
C.selectusers.user_idfromusersleftjoinordersonusers.user_id=orders.user_idwhereorders.user_idisnull
D.selectusers.user_idfromusersrightjoinordersonusers.user_id=orders.user_idwhereusers.user_idisnull
C、selectusers.user_idfromusersleftjoinordersonusers.user_id=orders.user_idwhereorders.user_idisnull