How to select distinct rows with a specified condition

问题:

Suppose there is a table

_ _ a 1 a 2 b 2 c 3 c 4 c 1 d 2 e 5 e 6 

How can I select distinct minimum value of all the rows of each group?

So the expected result here is:

_ _ a 1 b 2 c 1 d 2 e 5 

EDIT

My actual table contains more columns and I want to select them all. The rows differ only in the last column (the second one in the example). I'm new to SQL and possibly my question is ill-formed in it initial view.

The actual schema is:

| day | currency ('EUR', 'USD') | diff (integer) | id (foreign key) | 

The are duplicate pairs (day, currency) that differ by (diff, id). I want to see a table with uniquer pairs (day, currency) with a minimum diff from the original table.

Thanks!

回答1:

in your case it's as simple as this:

select column1, min(column2) as column2 from table group by column1 

for more than two columns I can suggest this:

select top 1 with ties     t.column1, t.column2, t.column3 from table as t order by row_number() over (partition by t.column1 order by t.column2) 

take a look at this post https://stackoverflow.com/a/13652861/1744834

回答2:

You can use the ranking function ROW_NUMBER() to do this with a CTE. Especially, if there are more column other than these two column, it will give the distict values like so:

;WITH RankedCTE AS (    SELECT *, ROW_NUMBER() OVER(PARTITION BY column1 ORDER BY Colmn2 ) rownum    FROM Table ) SELECT column1, column2 FROM RankedCTE WHERE rownum = 1; 

This will give you:

COLUMN1   COLUMN2    a         1    b         2    c         1    d         2    e         5 

SQL Fiddle Demo

回答3:

SELECT ColOne, Min(ColTwo) FROM Table GROUP BY ColOne ORDER BY ColOne

PS: not front of a,machine, but give above a try please.

回答4:

select MIN(col2),col1 from dbo.Table_1 group by col1 

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