MySQL MySQL根据一行的唯一性选择DISTINCT多列？
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MySQL Select DISTINCT multiple columns based on the uniqueness of one row?
提问by TK123
I'm trying to understand what this query does exactly:
我试图了解这个查询究竟做了什么：
SELECT DISTINCT `state`, `state_name` FROM `geo` ORDER BY `state_name` ASC
All I'm trying to do is select 2 columns (state and state_name), I want only unique rows that do not have duplicate values for the state field. I don't care if there are duplicate values in the state_name field.
我想要做的就是选择 2 列（state 和 state_name），我只想要状态字段没有重复值的唯一行。我不在乎 state_name 字段中是否有重复值。
Is my query checking both columns for uniqueness or just state?
我的查询是检查两列的唯一性还是仅检查状态？
回答by Chris Gessler
DISTINCT will return only distinct rows, so:
DISTINCT 将只返回不同的行，所以：
Is my query checking both columns for uniqueness or just state?
我的查询是检查两列的唯一性还是仅检查状态？
Both columns
两列
You could also switch to GROUP BY instead.
您也可以改用 GROUP BY。
SELECT `state`, `state_name` FROM `geo` group by 'state', 'state_name' ORDER BY `state_name` ASC
回答by Shan Plourde
It's checking for unique combinations of state and state_name. Distinct operates on all columns included in your select list.
它正在检查 state 和 state_name 的唯一组合。Distinct 对选择列表中包含的所有列进行操作。
To only include unique state values, just select distinct state
要仅包含唯一的状态值，只需选择不同的状态
