SQL-如何计算列的唯一组合 [英] SQL - how to count unique combination of columns

问题描述

我不确定是否可行，但是我想计算表中唯一值的数量.我知道要计算我做的唯一FolderID的数量:

I'm not sure if this is possible but I want to count the number of unique value in a table. I know to count the number of unique folderIDs I do:

select count(folderid) from folder

但是我想计算文件夹表中folderid和userid的唯一组合的数量.有办法吗?

but I want the count of the number of unique combination of folderid and userid in the folder table. Is there a way to do this?

推荐答案

select count(*) from (
  select distinct folderid, userid from folder
)

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