ORDER BY ROW_NUMBER

Question

UPD: thanks for all, topic closed, after sleeping I understand everything =)

I have a problem with understanding OVER clause and and ROW_NUMBER function. Simple tabl

Answer 1

You can certainly order by ROW_NUMBER column because the SELECT clause is evaluated before the ORDER BY clause. You can ORDER BY any column or column alias. This is why no error message was thrown (because it is valid).

SELECT name,  ROW_NUMBER() over (PARTITION BY name ORDER BY name) as number
FROM @table 
ORDER BY number

Evaluates to

name       number
---------- --------------------
John       1
pete       1
pete       2
John       2
pete       3

OP's second example of row_number is not correct.

SELECT AVG(mark) OVER(PARTITION BY name), name,  ROW_NUMBER() over (PARTITION BY name ORDER BY name) as number
FROM @table 
ORDER BY AVG(mark) OVER(PARTITION BY name), number

Returns as expected because AVG is the first sort column followed by number.

            name       number
----------- ---------- --------------------
11          pete       1
11          pete       2
11          pete       3
17          John       1
17          John       2

Change the query to number DESC and pete is still first however the row numbers are descending order.

            name       number
----------- ---------- --------------------
11          pete       3
11          pete       2
11          pete       1
17          John       2
17          John       1

SQL Order of operations

FROM clause
WHERE clause
GROUP BY clause
HAVING clause
SELECT clause
ORDER BY clause