MySQL 如何仅从一列中选择不同的值
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How to select distinct value from one column only
提问by user1810868
I have records as follows:
我有如下记录：
key | name
--------------
1111 | aa
1111 | bb
2222 | cc
I need to select the keyand namewhen the keyvalue is distinct. When I tried:
当值不key同时name，我需要选择和key。当我尝试：
select distinct key, name from table;
I got all the rows since the query takes distinct for the combination of the columns: keyand name. But, what I need is only distinct keyand I don't care about the name. I have a lot of records, so I need a practical method.
我得到了所有的行，因为查询对于列的组合是不同的：key和name。但是，我需要的只是不同的key，我不在乎name. 我有很多记录，所以我需要一个实用的方法。
回答by Justin
Query:
询问：
SELECT `key`, MAX(`name`) as name
FROM `table`
GROUP BY `key`
回答by fthiella
Why not just:
为什么不只是：
SELECT distinct key
FROM table
or
或者
SELECT key, name
FROM table
GROUP BY key
回答by systemboot
How about this:
这个怎么样：
select * from table group by key having count(key) = 1
回答by Bill Karwin
SELECT key, name FROM table GROUP BY key;
This returns one row for each distinct value of key, and the value of nameis arbitrarily chosen from the rows in that group. In practice, MySQL tends to return the value of name from the row physically stored first in the group, but that's not guaranteed.
这将为 的每个不同值返回一行key，并且 的值name是从该组中的行中任意选择的。在实践中，MySQL 倾向于从物理上首先存储在组中的行返回 name 的值，但这并不能保证。
As other answers show, you can put name into an aggregate expression.
正如其他答案所示，您可以将 name 放入聚合表达式中。
回答by amk
If you do not care about not groupped fields try this query -
如果您不关心未分组的字段，请尝试此查询 -
select key, name from table group by key order by name
MySQL lets selecting fields without using aggregate function.
MySQL 允许在不使用聚合函数的情况下选择字段。
order by namehelps to select first name from the group.
按名称排序有助于从组中选择名字。
