AND 6 GROUP BY month(created_at) 问题:对于CreditCard,结果为null。我试过COALESCE(sum(order_value),0)
month(created_atBY month(created_at), payment_method /*here is th
SET t_points=t_points+ (SELECT points from sites where url='$url') where username='$login_session'";如果子查询SELECT points from sites where url='$url'返回一些东西,那么查询就可以正常工作。如果不返回任何内容,则t_points中的前一个值将变为null。
如何编写更具