sql query distinct with Row_Number

Question

I am fighting with the distinct keyword in sql. I just want to display all row numbers of unique (distinct) values in a column & so I tried:

SELECT DISTINCT id, ROW_NUMBER() OVER (ORDER BY id) AS RowNum
FROM table
WHERE fid = 64

however the below code giving me the distinct values:

SELECT distinct id FROM table WHERE fid = 64

but when tried it with Row_Number.
then it is not working.

Answer 1

Use this:

SELECT *, ROW_NUMBER() OVER (ORDER BY id) AS RowNum FROM
    (SELECT DISTINCT id FROM table WHERE fid = 64) Base

and put the "output" of a query as the "input" of another.

Using CTE:

; WITH Base AS (
    SELECT DISTINCT id FROM table WHERE fid = 64
)

SELECT *, ROW_NUMBER() OVER (ORDER BY id) AS RowNum FROM Base

The two queries should be equivalent.

Technically you could

SELECT DISTINCT id, ROW_NUMBER() OVER (PARTITION BY id ORDER BY id) AS RowNum 
    FROM table
    WHERE fid = 64

but if you increase the number of DISTINCT fields, you have to put all these fields in the PARTITION BY, so for example

SELECT DISTINCT id, description,
    ROW_NUMBER() OVER (PARTITION BY id, description ORDER BY id) AS RowNum 
    FROM table
    WHERE fid = 64

I even hope you comprehend that you are going against standard naming conventions here, id should probably be a primary key, so unique by definition, so a DISTINCT would be useless on it, unless you coupled the query with some JOINs/UNION ALL...