Let's say:

I want to query colA, colB and colC in my table.

I want to see DISTINCT values but I don't want colA to be a criteria for distinction.

Omitting colA isn't an option.

What's the best way to structure that query?

解決方案

There are two cases here. Let's say you have the data

A B C (columns)

a b c1

a b c2

Taking distinct values of A, B gives just one result (a,b), with two values for column C.

So the question is do you want to see all values of C or just one value for each distinct value of columns A and B?

If you want to see just one value of C, then you can write

SELECT A, B, MAX(C) FROM YourTable

GROUP BY A, B

On the other hand, if you want to see all values for C then

SELECT DISTINCT A, B, C FROM YourTable WHERE ROW(A,B) IN

(SELECT A, B FROM YourTable

GROUP BY A, B)

gives you that. This last alternative is needed if there are other columns in the table.

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