为结果加入两个表?

I have 2 tables in a database person and order tables.

我在一个数据库person和order表中有两个表。

PERSON table:

人表:

PERSON_ID | NAME

ORDER table:

顺序表:

ORDER_ID | ORDER_NO | PERSON_ID

I need to display all the orders + a name of corresponding person if it exists, if not just order details.

我需要显示所有的订单+一个对应的人的名字，如果它存在的话，如果不只是订单的细节。

So far I got up to query:

到目前为止，我一直在查询:

SELECT ORDER_ID, ORDER_NO, order.PERSON_ID, NAME 
  FROM person, order 
 WHERE person.PERSON_ID = order.PERSON_ID AND 
       person.FIRST_NAME IS NOT NULL;

Which gives me orders only if the name is available whereas I need to display all the orders despite the fact if name is available or not.

只有当名称是可用的时候，才给我订单，而我需要显示所有的订单，尽管名称是否可用。

Any suggestions?

有什么建议吗?

1 个解决方案

#1

Yes, you can use LEFT JOIN for that:

是的，你可以使用左连接:

   SELECT o.order_id, o.order_no, o.person_id, p.name
     FROM `order` o
LEFT JOIN person p
       ON p.person_id = o.person_id AND p.FIRST_NAME IS NOT NULL

With LEFT JOIN if the name is null it will still give you the orders.

如果名称为空，那么它仍然会给您订单。

#1