mysql - 从具有 DISTINCT 字段的表中选择字段

Question

我有一张这种类型的桌子

| 用户 | 父母| 儿子 |

和

• 可以为 NULL 的父母和儿子的列。
• 用户列可以包含重复

我写了这个查询：

SELECT user, COALESCE(parents, 0) AS parentsEd, COALESCE(sons, 0) AS sonsEd 
  FROM my_table 
  ORDER BY (parentsEd + sonsEd) DESC

它有效！所以它给出了重复用户的结果。如何使用(parentsEd + sonsEd) DESC ORDER 拥有 DISTINC 用户？

Answer 1

在 order 子句之前使用GROUP BY，如果要先排序结果，然后将它们分组，然后使用 subselect

SELECT `user`, COALESCE(parents, 0) AS parentsEd, COALESCE(sons, 0) AS sonsEd
 FROM my_table GROUP BY `user` ORDER BY (parentsEd + sonsEd) DESC

SELECT DISTINCT `user`, COALESCE(parents, 0) AS parentsEd, COALESCE(sons, 0) AS sonsEd
 FROM my_table  ORDER BY (parentsEd + sonsEd) DESC


SELECT a.* FROM (
SELECT DISTINCT `user`, COALESCE(parents, 0) AS parentsEd, COALESCE(sons, 0) AS sonsEd
 FROM my_table  ORDER BY (parentsEd + sonsEd) DESC ) a GROUP BY a.`user`