从两个表中选择，其中链接列可以为空 [英] select from two tables where linked column can be null

问题描述

我在数据库中有两个表.表1包含一个可能为NULL的订单号.表2包含所有订单数据(包括订单号).

I have two tables in a database. Table 1 includes an order number which could be NULL. Table two contains all order data (including the order number).

现在，我想从表1中选择所有列，并从表2中选择所有订单数据.因此，如果表一中的某个条目不包含此订单号，则所有其他列均应为null.但是，如果确实包含订单号，我希望将其链接到第二张表并选择这些数据.

Now I want to select all columns from table 1 and all order data from table two. So if a certain entry in table one doesn't contains this order number, all other columns should be null. But if it does contain an order number I want it to be linked to the second table and have these data selected.

输出应类似于:

column1tab1 column2tab1 order_number product amount
 xx            yy            123      p1      2
 xx            yy            456      p3      4
 xx            yy            NULL    NULL    NULL
 xx            yy            789      p2      1
 etc...

我尝试了不同的方法，但是我只获得了所有带有订单号的行或全部为空的行，但是我无法同时获得它们.有人知道解决方案吗，所以我可以在一个查询中做到这一点?

I tried different things, but I only get all the rows with an order number or all with null, but I can't get them both at the same time. Does someone know a solution, so I can do this in one query?

推荐答案

您尝试了什么?一个简单的左联接就可以解决问题. 示例:

what did you try? A simple left join would do the trick. Example:

select *
from orders o left join orderdata od on o.orderId=od.orderid

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