After my cube is built, "SELECT COUNT(*) FROM table" gives the correct result. "SELECT COUNT(*) FROM table WHERE condition" also gives the correct result, but "SELECT COUNT(*) FILTER (WHERE condition) FROM table" gives the wrong result - as if there is no filter at all.
It is common to have multiple aggregates in one query, each with different conditions. Without the FILTER clause, we will have to write multiple queries then combine the results together.
