Question

I have a table with multiple entries and I have ordered it according to a sales criterion. So, if the entries are like:

Item  Sales
a     10
b     10
c     9
d     8
e     8
f     7

I want to extract the items with the highest and second highest number of sales. As such,
I would want to extract a, b and c.
Is there any function in PostgreSQL that can help with this?

Answer 1

To include all rows with one of the top two sales values, you could use the dense_rank() window function:

WITH x AS (
   SELECT *
         ,dense_rank() OVER (ORDER BY sales DESC) AS rnk
   FROM   tbl
   )
SELECT item, sales
FROM   x
WHERE  rnk < 3;

You need PostgreSQL 8.4 or later for that.

---

For older versions, you could:

SELECT *
FROM   tbl
JOIN   (
    SELECT sales
    FROM   tbl
    GROUP  BY 1
    ORDER  BY 1 DESC
    LIMIT  2
    ) t1 USING (sales)