从具有不同列数的两个表中选择* [英] select * from two tables with different # of columns

问题描述

如何从两个不同的表中选择不同的列，例如:

How would I select different columns from two different tables, such as:

SELECT username, email FROM `table1` 
UNION
 SELECT * FROM `table2` WHERE username = 'user1';

我收到错误"#1222 - The used SELECT statements have a different number of columns".据我了解，UNION无法正常工作，

I'm getting an error "#1222 - The used SELECT statements have a different number of columns". From what I understand UNION will not work,

有没有一种方法可以完成此操作，因为我需要不等数量的列和行，并且两个表中没有相互/相似的条目(即，user1未在表1中列出)?

Is there a way to accomplish this, since I would need unequal number of columns and rows and there are no mutual/similar entries in the two tables (i.e. user1 is not listed in table1)?

这不能在一个查询中完成吗?

Can this not be done in one query?

谢谢！

推荐答案

您可以使用别名fake缺少的列-例如

You can fake the missing columns using an alias - e.g.

 SELECT username, email, '' as name FROM `table1` 
 UNION
 SELECT username, email, name FROM `table2` 
 WHERE username = 'user1';

名称在表2中，但不在表1中

where name is in table2, but not in table1

除非您将UNIONS与JOINS混淆:

Unless you're confusing UNIONS with JOINS:

SELECT table1.*, table2.* FROM
table1 INNER JOIN table2
ON table1.username = table2.username

这将合并两个表，因此您将所有列都放在同一行.

this would merge both tables, so you get all the columns on the same row.

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