DROP TABLE IF EXISTS t1, t2;
CREATE TABLE t1 (id INTEGER);
CREATE TABLE t2 (id INTEGER);
INSERT INTO t1 (id) VALUES (1), (1), (1),(1);
INSERT INTO t1 (id) SELECT id FROM t1;
/* 8 */
INSERT INTO t1 (id) SELECT id FROM t1;
/* 12 */
INSERT INTO t1 (id) SELECT id FROM t1;
/* 16 */
INSERT INTO t1 (id) SELECT id FROM t1;
/* 20 */
INSERT INTO t1 (id) SELECT id FROM t1;
/* 24 */
INSERT INTO t1 SELECT id+1 FROM t1;
INSERT INTO t1 SELECT id+2 FROM t1;
INSERT INTO t1 SELECT id+4 FROM t1;
INSERT INTO t1 SELECT id+8 FROM t1;
INSERT INTO t1 SELECT id+16 FROM t1;
INSERT INTO t1 SELECT id+32 FROM t1;
INSERT INTO t1 SELECT id+64 FROM t1;
INSERT INTO t1 SELECT id+128 FROM t1;
INSERT INTO t1 SELECT id+256 FROM t1;
INSERT INTO t1 SELECT id+512 FROM t1;
SELECT AVG(DISTINCT id) FROM t1 GROUP BY id % 13;
AVG(DISTINCT id)
513.5000
508.0000
509.0000
510.0000
511.0000
512.0000
513.0000
514.0000
515.0000
516.0000
517.0000
511.5000
512.5000
SELECT SUM(DISTINCT id)/COUNT(DISTINCT id) FROM t1 GROUP BY id % 13;
SUM(DISTINCT id)/COUNT(DISTINCT id)
513.5000
508.0000
509.0000
510.0000
511.0000
512.0000
513.0000
514.0000
515.0000
516.0000
517.0000
511.5000
512.5000
INSERT INTO t1 SELECT id+1024 FROM t1;
INSERT INTO t1 SELECT id+2048 FROM t1;
INSERT INTO t1 SELECT id+4096 FROM t1;
INSERT INTO t1 SELECT id+8192 FROM t1;
INSERT INTO t2 SELECT id FROM t1 ORDER BY id*rand();
SELECT SUM(DISTINCT id) sm FROM t1;
sm
134225920
SELECT SUM(DISTINCT id) sm FROM t2;
sm
134225920
SELECT SUM(DISTINCT id) sm FROM t1 group by id % 13;
sm
10327590
10328851
10330112
10331373
10332634
10317510
10318770
10320030
10321290
10322550
10323810
10325070
10326330
SET max_heap_table_size=16384;
SHOW variables LIKE 'max_heap_table_size';
Variable_name	Value
max_heap_table_size	16384
SELECT SUM(DISTINCT id) sm FROM t1;
sm
134225920
SELECT SUM(DISTINCT id) sm FROM t2;
sm
134225920
SELECT SUM(DISTINCT id) sm FROM t1 GROUP BY id % 13;
sm
10327590
10328851
10330112
10331373
10332634
10317510
10318770
10320030
10321290
10322550
10323810
10325070
10326330
DROP TABLE t1;
DROP TABLE t2;