SELECT distinct field in Querydsl

Question

I would like to ask about how to make a SELECT Distinct on field in Querydsl 4. What is the best way to do this SQL request:

SELECT DISTINCT ON 
    (company_id, EXTRACT(MONTH FROM createddt), EXTRACT(YEAR FROM createddt)) id, 
    createddt 
FROM companystats 
ORDER BY company_id, 
    EXTRACT(MONTH FROM createddt) DESC,
    EXTRACT(YEAR FROM createddt) DESC,
    createddt DESC

Thanks.

Answer 1

Your SQL looks like a Postgres-Query. So, the best way would be to use distinctOn in com.querydsl.sql.postgresql.PostgreSQLQuery.

PostgreSQLQuery query = new PostgreSQLQuery(con);
query.select(companystats.id, companystats.createddt)
    .distinctOn(companystats.company_id, 
        companystats.createddt.month(), companystats.createddt.year())
    .from(companystats)
    .orderBy(companystats.createddt.month().desc(), 
             companystats.createddt.year().desc(),
             companystats.createddt.desc());