LunaQL docs are incomplete.
Reference
clauses
having

having

The having clause is used to filter out results based on a specified criteria:

posts.lunaql
query({
	from({
		posts: {
			groupBy(["user_id"]);
            having(["_count", ">", 1]);
		};
	});
});

You can use the same conditions you would normally have in your where clause:

posts.lunaql
query({
	from({
		posts: {
			having(["content", "like", "%Post%"]);
		};
	});
});