table_small zeros(10000000) zeros_mt(100000000) table_large zeros(100000000) zeros_mt(1000000000) size_large 1048576 10000000 size_small 1 16 1024 16384 SELECT count() FROM {table_large} WHERE rand64() IN (SELECT number FROM system.numbers LIMIT {size_small}) SELECT count() FROM {table_small} WHERE rand64() IN (SELECT number FROM system.numbers LIMIT {size_large})