关于多列的DISTINCT

Question

我有, SELECT DISTINCT (first),second,third FROM table

我想要的不仅是第一个是DISTINCT,第二个是DISTINCT,而第三个没有DISTINCT,我试着这样做.

SELECT DISTINCT (first,second),third FROM table

并结合更多的东西,但没有奏效.

Answer 1

SELECT  m.first, m.second, m.third -- and possibly other columns
FROM    (
        SELECT  DISTINCT  first, second
        FROM    mytable
        ) md
JOIN    mytable m
ON      m.id =
        (
        SELECT  id
        FROM    mytable mi
        WHERE   mi.first = md.first
                AND mi.second = md.second
        ORDER BY
                mi.first, mi.second, mi.third
        LIMIT 1
        )

(first, second, third)为此创建索引以快速工作.