QUALIFY clause - Amazon Redshift

QUALIFY clause

The QUALIFY clause filters results of a previously computed window function according to user‑specified search conditions. You can use the clause to apply filtering conditions to the result of a window function without using a subquery.

It is similar to the HAVING clause, which applies a condition to further filters rows from a WHERE clause. The difference between QUALIFY and HAVING is that filtered results from the QUALIFY clause could be based on the result of running window functions on the data. You can use both the QUALIFY and HAVING clauses in one query.

Syntax

QUALIFY condition
Note

If you're using the QUALIFY clause directly after the FROM clause, the FROM relation name must have an alias specified before the QUALIFY clause.

Examples

The examples in this section use the sample data below.

create table store_sales (ss_sold_date date, ss_sold_time time, ss_item text, ss_sales_price float); insert into store_sales values ('2022-01-01', '09:00:00', 'Product 1', 100.0), ('2022-01-01', '11:00:00', 'Product 2', 500.0), ('2022-01-01', '15:00:00', 'Product 3', 20.0), ('2022-01-01', '17:00:00', 'Product 4', 1000.0), ('2022-01-01', '18:00:00', 'Product 5', 30.0), ('2022-01-02', '10:00:00', 'Product 6', 5000.0), ('2022-01-02', '16:00:00', 'Product 7', 5.0);

The following example demonstrates how to find the two most expensive items sold after 12:00 each day.

SELECT * FROM store_sales ss WHERE ss_sold_time > time '12:00:00' QUALIFY row_number() OVER (PARTITION BY ss_sold_date ORDER BY ss_sales_price DESC) <= 2 ss_sold_date | ss_sold_time | ss_item | ss_sales_price --------------+--------------+-----------+---------------- 2022-01-01 | 17:00:00 | Product 4 | 1000 2022-01-01 | 18:00:00 | Product 5 | 30 2022-01-02 | 16:00:00 | Product 7 | 5

You can then find the last item sold on each day.

SELECT * FROM store_sales ss QUALIFY last_value(ss_item) OVER (PARTITION BY ss_sold_date ORDER BY ss_sold_time ASC ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING) = ss_item; ss_sold_date | ss_sold_time | ss_item | ss_sales_price --------------+--------------+-----------+---------------- 2022-01-01 | 18:00:00 | Product 5 | 30 2022-01-02 | 16:00:00 | Product 7 | 5

The following example returns the same result of the last item sold on each day but doesn't use the QUALIFY clause.

SELECT * FROM ( SELECT *, last_value(ss_item) OVER (PARTITION BY ss_sold_date ORDER BY ss_sold_time ASC ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING) ss_last_item FROM store_sales ss ) WHERE ss_last_item = ss_item; ss_sold_date | ss_sold_time | ss_item | ss_sales_price | ss_last_item --------------+--------------+-----------+----------------+-------------- 2022-01-02 | 16:00:00 | Product 7 | 5 | Product 7 2022-01-01 | 18:00:00 | Product 5 | 30 | Product 5