Sometimes when aggregating data with SQL, we’d love to add some additional filters. For instance, consider the following world bank data:

GDP per capita (current US$)

2009 2010 2011 2012
CA 40,764 47,465 51,791 52,409	
DE 40,270 40,408 44,355 42,598	
FR 40,488 39,448 42,578 39,759	
GB 35,455 36,573 38,927 38,649	
IT 35,724 34,673 36,988 33,814	
JP 39,473 43,118 46,204 46,548	
RU 8,616 10,710 13,324 14,091	
US 46,999 48,358 49,855 51,755

And the table structure:

CREATE TABLE countries (
 code CHAR(2) NOT NULL,
 year INT NOT NULL,
 gdp_per_capita DECIMAL(10, 2) NOT NULL
);

Now, let’s assume we’d like to find the number of countries with a GDP higher than 40,000 for each year.

With standard SQL:2003, and now also with the newly released PostgreSQL 9.4, we can now take advantage of the new FILTER clause, which allows us to write the following query:

SELECT
 year,
 count(*) FILTER (WHERE gdp_per_capita >= 40000)
FROM
 countries
GROUP BY
 year

The above query will now yield:

year count
------------
2012 4
2011 5
2010 4
2009 4

And that’s not it! As always, you can use any aggregate function also as a window function simply by adding an OVER() clause to the end:

SELECT
 year,
 code,
 gdp_per_capita,
 count(*) 
 FILTER (WHERE gdp_per_capita >= 40000) 
 OVER (PARTITION BY year)
FROM
 countries

The result would then look something like this:

year code gdp_per_capita count
------------------------------------
2009 CA 40764.00 4
2009 DE 40270.00 4
2009 FR 40488.00 4
2009 GB 35455.00 4

jOOQ 3.6 will also support the new FILTER clause for aggregate functions

Good news for jOOQ users. You can write the same query with jOOQ intuitively as such:

DSL.using(configuration)
 .select(
 COUNTRIES.YEAR,
 count().filterWhere(
 COUNTRIES.GDP_PER_CAPITA.ge(40000)
 ))
 .from(COUNTRIES)
 .groupBy(COUNTRIES.YEAR)
 .fetch();

… and

DSL.using(configuration)
 .select(
 COUNTRIES.YEAR,
 COUNTRIES.CODE,
 COUNTRIES.GDP_PER_CAPITA
 count().filterWhere(
 COUNTRIES.GDP_PER_CAPITA.ge(40000))
 .over(partitionBy(COUNTRIES.YEAR)))
 .from(COUNTRIES)
 .fetch();

And the best thing is that jOOQ (as usual) emulates the above clause for you if you’re not using PostgreSQL. The equivalent query would be:

SELECT
 year,
 count(CASE WHEN gdp_per_capita >= 40000 THEN 1 END)
FROM
 countries
GROUP BY
 year

👁 jooq-the-best-way-to-write-sql-in-java-small

Read more about what’s new in PostgreSQL 9.4 here