DENSE_RANK window function - Amazon Redshift
SyntaxArgumentsReturn typeExamples

DENSE_RANK window function

The DENSE_RANK window function determines the rank of a value in a group of values, based on the ORDER BY expression in the OVER clause. If the optional PARTITION BY clause is present, the rankings are reset for each group of rows. Rows with equal values for the ranking criteria receive the same rank. The DENSE_RANK function differs from RANK in one respect: if two or more rows tie, there is no gap in the sequence of ranked values. For example, if two rows are ranked 1, the next rank is 2.

You can have ranking functions with different PARTITION BY and ORDER BY clauses in the same query.

Syntax

DENSE_RANK() OVER
(
[ PARTITION BY expr_list ]
[ ORDER BY order_list ]
)

Arguments

( )

The function takes no arguments, but the empty parentheses are required.

OVER

The window clauses for the DENSE_RANK function.

PARTITION BY expr_list

(Optional) One or more expressions that define the window.

ORDER BY order_list

(Optional) The expression on which the ranking values are based. If no PARTITION BY is specified, ORDER BY uses the entire table. If ORDER BY is omitted, the return value is 1 for all rows.

If ORDER BY doesn't produce a unique ordering, the order of the rows is nondeterministic. For more information, see Unique ordering of data for window functions.

Return type

INTEGER

Examples

The following examples use the sample table for window functions. For more information, see Sample table for window function examples.

The following example orders the table by the quantity sold and assigns both a dense rank and a regular rank to each row. The results are sorted after the window function results are applied. 

SELECT salesid, qty,
DENSE_RANK() OVER(ORDER BY qty DESC) AS d_rnk,
RANK() OVER(ORDER BY qty DESC) AS rnk
FROM winsales
ORDER BY 2,1;

+---------+-----+-------+-----+
| salesid | qty | d_rnk | rnk |
+---------+-----+-------+-----+
|   10001 |  10 |     5 |   8 |
|   10006 |  10 |     5 |   8 |
|   30001 |  10 |     5 |   8 |
|   40005 |  10 |     5 |   8 |
|   30003 |  15 |     4 |   7 |
|   20001 |  20 |     3 |   4 |
|   20002 |  20 |     3 |   4 |
|   30004 |  20 |     3 |   4 |
|   10005 |  30 |     2 |   2 |
|   30007 |  30 |     2 |   2 |
|   40001 |  40 |     1 |   1 |
+---------+-----+-------+-----+

Note the difference in rankings assigned to the same set of rows when the DENSE_RANK and RANK functions are used side by side in the same query.

The following example partitions the table by sellerid, orders each partition by the quantity, and assigns a dense rank to each row. The results are sorted after the window function results are applied. 

SELECT salesid, sellerid, qty,
DENSE_RANK() OVER(PARTITION BY sellerid ORDER BY qty DESC) AS d_rnk
FROM winsales
ORDER BY 2,3,1;

+---------+----------+-----+-------+
| salesid | sellerid | qty | d_rnk |
+---------+----------+-----+-------+
|   10001 |        1 |  10 |     2 |
|   10006 |        1 |  10 |     2 |
|   10005 |        1 |  30 |     1 |
|   20001 |        2 |  20 |     1 |
|   20002 |        2 |  20 |     1 |
|   30001 |        3 |  10 |     4 |
|   30003 |        3 |  15 |     3 |
|   30004 |        3 |  20 |     2 |
|   30007 |        3 |  30 |     1 |
|   40005 |        4 |  10 |     2 |
|   40001 |        4 |  40 |     1 |
+---------+----------+-----+-------+

To successfully use the last example, use the following command to insert a row into the WINSALES table. This row has the same buyerid, sellerid, and qtysold as another row. This will cause two rows to tie in the last example and thus will show the difference between the DENSE_RANK and RANK functions.

INSERT INTO winsales VALUES(30009, '2/2/2003', 3, 'b', 20, NULL);

The following example partitions the table by buyerid and sellerid, orders each partition by the quantity, and assigns both a dense rank and a regular rank to each row. The results are sorted after the window function is applied. 

SELECT salesid, sellerid, qty, buyerid,
DENSE_RANK() OVER(PARTITION BY buyerid, sellerid ORDER BY qty DESC) AS d_rnk,
RANK() OVER (PARTITION BY buyerid, sellerid ORDER BY qty DESC) AS rnk
FROM winsales
ORDER BY rnk;

+---------+----------+-----+---------+-------+-----+
| salesid | sellerid | qty | buyerid | d_rnk | rnk |
+---------+----------+-----+---------+-------+-----+
|   20001 |        2 |  20 | b       |     1 |   1 |
|   30007 |        3 |  30 | c       |     1 |   1 |
|   10006 |        1 |  10 | c       |     1 |   1 |
|   10005 |        1 |  30 | a       |     1 |   1 |
|   20002 |        2 |  20 | c       |     1 |   1 |
|   30009 |        3 |  20 | b       |     1 |   1 |
|   40001 |        4 |  40 | a       |     1 |   1 |
|   30004 |        3 |  20 | b       |     1 |   1 |
|   10001 |        1 |  10 | c       |     1 |   1 |
|   40005 |        4 |  10 | a       |     2 |   2 |
|   30003 |        3 |  15 | b       |     2 |   3 |
|   30001 |        3 |  10 | b       |     3 |   4 |
+---------+----------+-----+---------+-------+-----+