我想从名字表中拉first_name,但只有当users_id在订单表和order_num = 1,但我不断收到错误。MYSQL加入与错误
SELECT first_name
FROM customers
LEFT JOIN orders
ON orders.order_id = customers.cust_id
AND orders.order_num = 1
,但我的查询返回多个值,而不只是一个,喜欢它忽略orders.order_num=1
- 没有我的查询看的权利,或者是有什么我做错了吗?
也许将只包括记录这个图表可以有所帮助:http://stackoverflow.com/questions/4715677/difference-between-left-join-and-right-join-in-sql-server/4715847#4715847 –