编写一个 SQL 查询,找出所有从不订购任何东西的客户。 Customers 表: +---+---+ | Id | Name | +---+---+ | 1 | Joe | | 2 | Henry | | 3 | Sam | | 4 | Max | +---+---+ Orders 表: +---+---+ | Id | CustomerId | +---+---+ | 1 | 3 | | 2 | 1 | +--...
那就要通过使用union来实现,具体实现SQL语句如下 select classa.id as aid,classb.id as bid from classa left join classb on classa.id = classb.id union select classa.id as aid,classb.id as bid from classa right join classb on classa.id = classb.id; 到此这篇关于SQL删除重复的电子邮...