Add a listagg/groupconcat function to CriteriaBuilder

[AleksNo]

Hi, sometimes i miss a listagg function in JPA. It is nice for summarizing some lists and present them to the user.

A good explanation what it does is here: https://www.w3resource.com/mysql/aggregate-functions-and-grouping/aggregate-functions-and-grouping-group_concat.php

The syntax would be: Expression listagg(Expression expr, String separator)

The usage would be: cb.listagg(MyEntity_.stringValue, ", ");

And a kind of distinctlistagg(Expression expr, String separator) would be nice too. It can happen that the concatenated String contains duplicates. They should be removed with distinctlistagg.

Greetings

[gavinking]

This seems like a feature that's very specific to MySQL, and should not be added to JPA.

I believe this issue should be closed.

[beikov]

It's not specific to MySQL. The big vendors all offer the SQL standard LISTAGG or some vendor specific version of it. In general, the SQL standard calls these kinds of functions "ordered set-aggregate functions" and I think that especially LISTAGG is one of the functions that is really useful.

[gavinking]

SQL standard LISTAGG

My bad, I was wrong.

[beikov]

FWIW Hibernate 6.0 supports listagg in HQL. If anyone is willing to work on the spec parts, Hibernate can serve as a compatible implementation.