SET optimize_use_implicit_projections = 0; -- the work for scalar subquery is properly accounted: SET max_rows_to_read = 1000000; SELECT 1 = (SELECT count() FROM test.hits WHERE NOT ignore(AdvEngineID)); -- { serverError TOO_MANY_ROWS } -- the work for subquery in IN is properly accounted: SET max_rows_to_read = 1000000; SELECT 1 IN (SELECT count() FROM test.hits WHERE NOT ignore(AdvEngineID)); -- { serverError TOO_MANY_ROWS } -- this query reads from the table twice: SET max_rows_to_read = 15000000; SELECT count() IN (SELECT count() FROM test.hits WHERE NOT ignore(AdvEngineID)) FROM test.hits WHERE NOT ignore(AdvEngineID); -- { serverError TOO_MANY_ROWS } -- the resources are properly accounted even if the subquery is evaluated in advance to facilitate the index analysis. -- this query is using index and filter out the second reading pass. SET max_rows_to_read = 1000000; SELECT count() FROM test.hits WHERE CounterID > (SELECT count() FROM test.hits WHERE NOT ignore(AdvEngineID)); -- { serverError TOO_MANY_ROWS } -- this query is using index but have to read all the data twice. SET max_rows_to_read = 10000000; SELECT count() FROM test.hits WHERE CounterID < (SELECT count() FROM test.hits WHERE NOT ignore(AdvEngineID)); -- { serverError TOO_MANY_ROWS }