[英]MySql - use of ALIAS for multiple columns
I saw the following code: 我看到了以下代码:
SELECT
u.ID, u.username, u.active, u.email, u.admin, u.banned,
u.name AS groupmemberships
FROM users u
WHERE u.ID={$uid}
and was wondering where the official documentation about aliasing multiple columns was. 并想知道关于多列混叠的官方文档在哪里。 W3schools (not the best source) as the only place where I found "documentation" in the following way:
W3schools(不是最好的来源)是我通过以下方式找到“文档”的唯一地方:
SELECT column_name(s) FROM table_name AS alias_name;
http://www.w3schools.com/sql/sql_alias.asp http://www.w3schools.com/sql/sql_alias.asp
I would appreciate a link to official documentation so I can look it over. 我希望获得官方文档的链接,以便我可以查看。
You can't use the same alias for multiple columns, but you can concatenate values and give the result an alias: 您不能对多个列使用相同的别名,但您可以连接值并为结果指定别名:
SELECT
u.ID, u.username, u.active, u.email, u.admin, u.banned,
u.name + u.username AS groupmemberships
FROM users u
If this is what you want, then check here for how to deal with null values. 如果这是你想要的,那么请在这里检查如何处理空值。
您可以使用concat
函数为多列获取单个别名,
select concat(first_name, ' ', last_name) as employee_name from user;
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