Rank Function inside case statement

Question

I am trying to use Rank Function inside a case statement and give where rank_number = 1 , it's throwing error as unexpected where Condition. Can some one help me how to assign rank in where clause inside case statement

Answer 1

You can't use the RANK() analytic function (or any other one, for that matter) in the WHERE clause of a query. The results of the rank computation are not yet available. But they are available in the SELECT clause or the ORDER BY clause. One workaround would be to subquery:

SELECT *
FROM
(
    SELECT t.*, RANK() OVER (ORDER BY blah) rnk
    FROM yourTable t
) s
WHERE rnk = 1;

Some databases support a QUALIFY clause, where it is possible to use analytic functions. Assuming you are using something like Teradata or BigQuery, you could use:

SELECT *
FROM yourTable
WHERE 1 = 1
QUALIFY RANK() OVER (ORDER BY blah) = 1;