I would like to check if a query (filter) is not empty, something like this in PostgreSQL:
select EXISTS(select 1 from tab where tab.name = 'abc')
https://www.postgresql.org/docs/11/functions-subquery.html
My current approach in AQL is:
RETURN LENGTH(for d in tab filter d.name = 'abc' RETURN 1) > 0
The sub-query FOR d IN tab FILTER d.name == 'abc' may find a matching document early on, but will continue looking for more because there is no limit defined. Therefore, I would recommend:
RETURN LENGTH(FOR d IN tab FILTER d.name == 'abc' LIMIT 1 RETURN true) > 0
This would return [ true ] as query result.
You could also RETURN d starting from v3.4.0. The optimizer rule optimize-subqueries recognizes the pattern LENGTH(... RETURN doc) and replaces doc with a constant value true.
