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QUALIFY clause
Applies to ✅ Open Source Edition ✅ Express Edition ✅ Professional Edition ✅ Enterprise Edition
A select few dialects support a very useful QUALIFY clause, which can be used to filter using window functions without having to nest the window function calculation in a derived table.
For example, if you do not have access to the WITH TIES clause, you could easily emulate it like this. The following query finds the top 5 author WITH TIES, counting their books:
SELECT AUTHOR_ID, count(*) FROM BOOK GROUP BY AUTHOR_ID QUALIFY rank() OVER (ORDER BY count(*) DESC) <= 5 ORDER BY count(*) DESC
create.select(BOOK.AUTHOR_ID, count())
.from(BOOK)
.groupBy(BOOK.AUTHOR_ID)
.qualify(rank().over(orderBy(count().desc())).le(5))
.orderBy(count().desc())
.fetch();
Dialect support
This example using jOOQ:
select(AUTHOR.ID).from(AUTHOR).qualify(rank().over(orderBy(AUTHOR.ID)).le(10))
Translates to the following dialect specific expressions:
Aurora Postgres, CockroachDB, MemSQL, Postgres, SQLite, Trino, Vertica, YugabyteDB
SELECT t.ID ID
FROM (
SELECT
*,
(rank() OVER (ORDER BY AUTHOR.ID) <= 10) w0
FROM AUTHOR
) t
WHERE w0
BigQuery
SELECT AUTHOR.ID FROM AUTHOR WHERE TRUE QUALIFY rank() OVER (ORDER BY AUTHOR.ID) <= 10
ClickHouse, Databricks, DuckDB, Exasol, H2, Snowflake, Teradata
SELECT AUTHOR.ID FROM AUTHOR QUALIFY rank() OVER (ORDER BY AUTHOR.ID) <= 10
DB2, SQLDataWarehouse, SQLServer, Sybase
SELECT t.ID ID
FROM (
SELECT
*,
CASE
WHEN rank() OVER (ORDER BY AUTHOR.ID) <= 10 THEN 1
WHEN NOT (rank() OVER (ORDER BY AUTHOR.ID) <= 10) THEN 0
END w0
FROM AUTHOR
) t
WHERE w0 = 1
Firebird
SELECT t.ID ID
FROM (
SELECT
AUTHOR.ID,
AUTHOR.FIRST_NAME,
AUTHOR.LAST_NAME,
AUTHOR.DATE_OF_BIRTH,
AUTHOR.YEAR_OF_BIRTH,
AUTHOR.DISTINGUISHED,
CASE
WHEN rank() OVER (ORDER BY AUTHOR.ID) <= 10 THEN 1
WHEN NOT (rank() OVER (ORDER BY AUTHOR.ID) <= 10) THEN 0
END w0
FROM AUTHOR
) t
WHERE w0 = 1
Hana
SELECT t.ID ID
FROM (
SELECT
*,
CASE
WHEN rank() OVER (ORDER BY AUTHOR.ID) <= 10 THEN TRUE
WHEN NOT (rank() OVER (ORDER BY AUTHOR.ID) <= 10) THEN FALSE
END w0
FROM AUTHOR
) t
WHERE w0 = TRUE
Informix
SELECT t.ID ID
FROM (
SELECT
*,
CASE
WHEN rank() OVER (ORDER BY AUTHOR.ID) <= 10 THEN CAST('t' AS boolean)
WHEN NOT (rank() OVER (ORDER BY AUTHOR.ID) <= 10) THEN CAST('f' AS boolean)
END w0
FROM AUTHOR
) t
WHERE w0
MariaDB, MySQL, Oracle
SELECT t.ID ID
FROM (
SELECT
AUTHOR.ID,
AUTHOR.FIRST_NAME,
AUTHOR.LAST_NAME,
AUTHOR.DATE_OF_BIRTH,
AUTHOR.YEAR_OF_BIRTH,
AUTHOR.DISTINGUISHED,
(rank() OVER (ORDER BY AUTHOR.ID) <= 10) w0
FROM AUTHOR
) t
WHERE w0
Redshift
SELECT AUTHOR.ID FROM AUTHOR WHERE 1 = 1 QUALIFY rank() OVER (ORDER BY AUTHOR.ID) <= 10
ASE, Access, Aurora MySQL, Derby, HSQLDB
/* UNSUPPORTED */
Generated with jOOQ 3.21. Support in older jOOQ versions may differ. Translate your own SQL on our website
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