Please note that for HSQLDB to join with function results the syntax is

SELECT * 
FROM TheTable t 
INNER JOIN TABLE(splitMe('1,2,3')) as ids
ON t.id = ids.value

The TABLE(...) syntax seems to be specific to HSQLDB.

Currently when using

RelationalFunctionCall.create(Integer.class, "splitMe", "1,2,3")

I'm getting

SELECT * 
FROM TheTable t 
INNER JOIN splitMe('1,2,3') as ids
ON t.id = ids.value

which fails in HSQLDB.
Of course above syntax works in MSSQL for example.

QueryDSL could wrap with TABLE(...) in JOIN statements or there should be an easy way to do that.

As a workaround I extend RelationalFunctionCall class and override getTemplate method to

return new TemplateFactory('\\').create("TABLE(" + super.getTemplate().toString() + ")");

which is ugly.