SET @@internal_tmp_mem_storage_engine = TempTable;
CREATE TABLE t_int (c INT);
CREATE TABLE t_char (c CHAR(20));
CREATE TABLE t_varchar (c VARCHAR(20));
CREATE TABLE t_text (c TEXT);
CREATE TABLE t_blob (c BLOB);
CREATE TABLE t_json (c JSON);
INSERT INTO t_int VALUES
(1),
(2),
(2),
(3),
(4),
(NULL);
INSERT INTO t_char VALUES
('abcde'),
('fghij'),
('fghij'),
('klmno  '),
('stxyz'),
(''),
(NULL);
INSERT INTO t_varchar VALUES
('abcde'),
('fghij'),
('fghij'),
('klmno  '),
('stxyz'),
(''),
(NULL);
INSERT INTO t_text VALUES
('abcde'),
('fghij'),
('fghij'),
('klmno  '),
('stxyz'),
(''),
(NULL);
INSERT INTO t_blob VALUES
('abcde'),
('fghij'),
('fghij'),
('klmno  '),
('stxyz'),
(''),
(NULL);
INSERT INTO t_json VALUES
('{"k1": "value", "k2": [10, 20]}'),
('["hot", "cold"]'),
('["hot", "cold"]'),
('["a", "b", 1]'),
('{"key": "value"}'),
(NULL);
SHOW STATUS LIKE 'Created_tmp_tables';
Variable_name	Value
Created_tmp_tables	0
SHOW STATUS LIKE 'Created_tmp_disk_tables';
Variable_name	Value
Created_tmp_disk_tables	0
# ---------------------------------------------------------------------
# Scenario 1:
#
SELECT DISTINCT * FROM
t_int AS t1,
t_int AS t2;
c	c
1	1
1	2
1	3
1	4
1	NULL
2	1
2	2
2	3
2	4
2	NULL
3	1
3	2
3	3
3	4
3	NULL
4	1
4	2
4	3
4	4
4	NULL
NULL	1
NULL	2
NULL	3
NULL	4
NULL	NULL
SELECT DISTINCT * FROM
t_char AS t1,
t_char AS t2;
c	c
	
	NULL
	abcde
	fghij
	klmno
	stxyz
NULL	
NULL	NULL
NULL	abcde
NULL	fghij
NULL	klmno
NULL	stxyz
abcde	
abcde	NULL
abcde	abcde
abcde	fghij
abcde	klmno
abcde	stxyz
fghij	
fghij	NULL
fghij	abcde
fghij	fghij
fghij	klmno
fghij	stxyz
klmno	
klmno	NULL
klmno	abcde
klmno	fghij
klmno	klmno
klmno	stxyz
stxyz	
stxyz	NULL
stxyz	abcde
stxyz	fghij
stxyz	klmno
stxyz	stxyz
SELECT DISTINCT * FROM
t_varchar AS t1,
t_varchar AS t2;
c	c
	
	NULL
	abcde
	fghij
	klmno  
	stxyz
NULL	
NULL	NULL
NULL	abcde
NULL	fghij
NULL	klmno  
NULL	stxyz
abcde	
abcde	NULL
abcde	abcde
abcde	fghij
abcde	klmno  
abcde	stxyz
fghij	
fghij	NULL
fghij	abcde
fghij	fghij
fghij	klmno  
fghij	stxyz
klmno  	
klmno  	NULL
klmno  	abcde
klmno  	fghij
klmno  	klmno  
klmno  	stxyz
stxyz	
stxyz	NULL
stxyz	abcde
stxyz	fghij
stxyz	klmno  
stxyz	stxyz
SELECT DISTINCT * FROM
t_text AS t1,
t_text AS t2;
c	c
	
	NULL
	abcde
	fghij
	klmno  
	stxyz
NULL	
NULL	NULL
NULL	abcde
NULL	fghij
NULL	klmno  
NULL	stxyz
abcde	
abcde	NULL
abcde	abcde
abcde	fghij
abcde	klmno  
abcde	stxyz
fghij	
fghij	NULL
fghij	abcde
fghij	fghij
fghij	klmno  
fghij	stxyz
klmno  	
klmno  	NULL
klmno  	abcde
klmno  	fghij
klmno  	klmno  
klmno  	stxyz
stxyz	
stxyz	NULL
stxyz	abcde
stxyz	fghij
stxyz	klmno  
stxyz	stxyz
SELECT DISTINCT * FROM
t_blob AS t1,
t_blob AS t2;
c	c
	
	NULL
	abcde
	fghij
	klmno  
	stxyz
NULL	
NULL	NULL
NULL	abcde
NULL	fghij
NULL	klmno  
NULL	stxyz
abcde	
abcde	NULL
abcde	abcde
abcde	fghij
abcde	klmno  
abcde	stxyz
fghij	
fghij	NULL
fghij	abcde
fghij	fghij
fghij	klmno  
fghij	stxyz
klmno  	
klmno  	NULL
klmno  	abcde
klmno  	fghij
klmno  	klmno  
klmno  	stxyz
stxyz	
stxyz	NULL
stxyz	abcde
stxyz	fghij
stxyz	klmno  
stxyz	stxyz
SELECT DISTINCT * FROM
t_json AS t1,
t_json AS t2;
c	c
NULL	NULL
NULL	["a", "b", 1]
NULL	["hot", "cold"]
NULL	{"k1": "value", "k2": [10, 20]}
NULL	{"key": "value"}
["a", "b", 1]	NULL
["a", "b", 1]	["a", "b", 1]
["a", "b", 1]	["hot", "cold"]
["a", "b", 1]	{"k1": "value", "k2": [10, 20]}
["a", "b", 1]	{"key": "value"}
["hot", "cold"]	NULL
["hot", "cold"]	["a", "b", 1]
["hot", "cold"]	["hot", "cold"]
["hot", "cold"]	{"k1": "value", "k2": [10, 20]}
["hot", "cold"]	{"key": "value"}
{"k1": "value", "k2": [10, 20]}	NULL
{"k1": "value", "k2": [10, 20]}	["a", "b", 1]
{"k1": "value", "k2": [10, 20]}	["hot", "cold"]
{"k1": "value", "k2": [10, 20]}	{"k1": "value", "k2": [10, 20]}
{"k1": "value", "k2": [10, 20]}	{"key": "value"}
{"key": "value"}	NULL
{"key": "value"}	["a", "b", 1]
{"key": "value"}	["hot", "cold"]
{"key": "value"}	{"k1": "value", "k2": [10, 20]}
{"key": "value"}	{"key": "value"}
# ---------------------------------------------------------------------
# Scenario 2:
#
SELECT c,COUNT(*) FROM t_int GROUP BY c;
c	COUNT(*)
1	1
2	2
3	1
4	1
NULL	1
SELECT c,COUNT(*) FROM t_char GROUP BY c;
c	COUNT(*)
	1
NULL	1
abcde	1
fghij	2
klmno	1
stxyz	1
SELECT c,COUNT(*) FROM t_varchar GROUP BY c;
c	COUNT(*)
	1
NULL	1
abcde	1
fghij	2
klmno  	1
stxyz	1
SELECT c,COUNT(*) FROM t_text GROUP BY c;
c	COUNT(*)
	1
NULL	1
abcde	1
fghij	2
klmno  	1
stxyz	1
SELECT c,COUNT(*) FROM t_blob GROUP BY c;
c	COUNT(*)
	1
NULL	1
abcde	1
fghij	2
klmno  	1
stxyz	1
SELECT c,COUNT(*) FROM t_json GROUP BY c;
c	COUNT(*)
NULL	1
["a", "b", 1]	1
["hot", "cold"]	2
{"k1": "value", "k2": [10, 20]}	1
{"key": "value"}	1
SHOW STATUS LIKE 'Created_tmp_tables';
Variable_name	Value
Created_tmp_tables	12
SHOW STATUS LIKE 'Created_tmp_disk_tables';
Variable_name	Value
Created_tmp_disk_tables	0
DROP TABLE t_int;
DROP TABLE t_char;
DROP TABLE t_varchar;
DROP TABLE t_text;
DROP TABLE t_blob;
DROP TABLE t_json;
CREATE TABLE t_pk (
pk INT NOT NULL,
PRIMARY KEY (pk)
);
INSERT INTO t_pk VALUES
(1),
(2),
(3);
SELECT COUNT(t_pk.pk) FROM t_pk
WHERE 1 IN (SELECT 1 FROM t_pk AS SQ2_alias1
WHERE 1 IN (SELECT 1 FROM t_pk AS C_SQ1_alias1)
);
COUNT(t_pk.pk)
3
DROP TABLE t_pk;
SET @@internal_tmp_mem_storage_engine = default;