drop table if exists t1,t2,t3;
CREATE TABLE t1 (id int,facility char(20));
CREATE TABLE t2 (facility char(20));
INSERT INTO t1 VALUES (NULL,NULL);
INSERT INTO t1 VALUES (-1,'');
INSERT INTO t1 VALUES (0,'');
INSERT INTO t1 VALUES (1,'/L');
INSERT INTO t1 VALUES (2,'A01');
INSERT INTO t1 VALUES (3,'ANC');
INSERT INTO t1 VALUES (4,'F01');
INSERT INTO t1 VALUES (5,'FBX');
INSERT INTO t1 VALUES (6,'MT');
INSERT INTO t1 VALUES (7,'P');
INSERT INTO t1 VALUES (8,'RV');
INSERT INTO t1 VALUES (9,'SRV');
INSERT INTO t1 VALUES (10,'VMT');
INSERT INTO t2 SELECT DISTINCT FACILITY FROM t1;
select id from t1 group by id;
id
NULL
-1
0
1
2
3
4
5
6
7
8
9
10
select * from t1 order by id;
id	facility
NULL	NULL
-1	
0	
1	/L
2	A01
3	ANC
4	F01
5	FBX
6	MT
7	P
8	RV
9	SRV
10	VMT
select id-5,facility from t1 order by "id-5";
id-5	facility
NULL	NULL
-6	
-5	
-4	/L
-3	A01
-2	ANC
-1	F01
0	FBX
1	MT
2	P
3	RV
4	SRV
5	VMT
select id,concat(facility) from t1 group by id ;
id	concat(facility)
NULL	NULL
-1	
0	
1	/L
2	A01
3	ANC
4	F01
5	FBX
6	MT
7	P
8	RV
9	SRV
10	VMT
select id+0 as a,max(id),concat(facility) as b from t1 group by a order by b desc,a;
a	max(id)	b
10	10	VMT
9	9	SRV
8	8	RV
7	7	P
6	6	MT
5	5	FBX
4	4	F01
3	3	ANC
2	2	A01
1	1	/L
-1	-1	
0	0	
NULL	NULL	NULL
select id >= 0 and id <= 5 as grp,count(*) from t1 group by grp;
grp	count(*)
0	7
1	6
SELECT DISTINCT FACILITY FROM t1;
FACILITY
NULL

/L
A01
ANC
F01
FBX
MT
P
RV
SRV
VMT
SELECT FACILITY FROM t2;
FACILITY
NULL

/L
A01
ANC
F01
FBX
MT
P
RV
SRV
VMT
SELECT count(*) from t1,t2 where t1.facility=t2.facility;
count(*)
12
select count(facility) from t1;
count(facility)
12
select count(*) from t1;
count(*)
13
select count(*) from t1 where facility IS NULL;
count(*)
1
select count(*) from t1 where facility = NULL;
count(*)
0
select count(*) from t1 where facility IS NOT NULL;
count(*)
12
select count(*) from t1 where id IS NULL;
count(*)
1
select count(*) from t1 where id IS NOT NULL;
count(*)
12
drop table t1,t2;
CREATE TABLE t1 (UserId int(11) DEFAULT '0' NOT NULL);
INSERT INTO t1 VALUES (20);
INSERT INTO t1 VALUES (27);
SELECT UserId FROM t1 WHERE Userid=22;
UserId
SELECT UserId FROM t1 WHERE UserId=22 group by Userid;
UserId
SELECT DISTINCT UserId FROM t1 WHERE UserId=22 group by Userid;
UserId
SELECT DISTINCT UserId FROM t1 WHERE UserId=22;
UserId
drop table t1;
CREATE TABLE t1 (a int(10) unsigned not null primary key,b int(10) unsigned);
INSERT INTO t1 VALUES (1,1),(2,1);
CREATE TABLE t2 (a int(10) unsigned not null, key (A));
INSERT INTO t2 VALUES (1),(2);
CREATE TABLE t3 (a int(10) unsigned, key(A), b text);
INSERT INTO t3 VALUES (1,'1'),(2,'2');
SELECT DISTINCT t3.b FROM t3,t2,t1 WHERE t3.a=t1.b AND t1.a=t2.a;
b
1
INSERT INTO t2 values (1),(2),(3);
INSERT INTO t3 VALUES (1,'1'),(2,'2'),(1,'1'),(2,'2');
explain SELECT distinct t3.a FROM t3,t2,t1 WHERE t3.a=t1.b AND t1.a=t2.a;
table	type	possible_keys	key	key_len	ref	rows	Extra
t3	index	a	a	5	NULL	6	Using index; Using temporary
t2	index	a	a	4	NULL	5	Using index; Distinct
t1	eq_ref	PRIMARY	PRIMARY	4	t2.a	1	where used; Distinct
SELECT distinct t3.a FROM t3,t2,t1 WHERE t3.a=t1.b AND t1.a=t2.a;
a
1
create temporary table t4 select * from t3;
insert into t3 select * from t4;
insert into t4 select * from t3;
insert into t3 select * from t4;
insert into t4 select * from t3;
insert into t3 select * from t4;
insert into t4 select * from t3;
insert into t3 select * from t4;
explain select distinct t1.a from t1,t3 where t1.a=t3.a;
table	type	possible_keys	key	key_len	ref	rows	Extra
t1	index	PRIMARY	PRIMARY	4	NULL	2	Using index; Using temporary
t3	ref	a	a	5	t1.a	10	Using index; Distinct
select distinct t1.a from t1,t3 where t1.a=t3.a;
a
1
2
select distinct 1 from t1,t3 where t1.a=t3.a;
1
1
drop table t1,t2,t3,t4;
CREATE TABLE t1 (name varchar(255));
INSERT INTO t1 VALUES ('aa'),('ab'),('ac'),('ad'),('ae');
SELECT DISTINCT * FROM t1 LIMIT 2;
name
aa
ab
SELECT DISTINCT name FROM t1 LIMIT 2;
name
aa
ab
SELECT DISTINCT 1 FROM t1 LIMIT 2;
1
1
drop table t1;
CREATE TABLE t1 (
ID int(11) NOT NULL auto_increment,
NAME varchar(75) DEFAULT '' NOT NULL,
LINK_ID int(11) DEFAULT '0' NOT NULL,
PRIMARY KEY (ID),
KEY NAME (NAME),
KEY LINK_ID (LINK_ID)
);
INSERT INTO t1 (ID, NAME, LINK_ID) VALUES (1,'Mike',0),(2,'Jack',0),(3,'Bill',0);
CREATE TABLE t2 (
ID int(11) NOT NULL auto_increment,
NAME varchar(150) DEFAULT '' NOT NULL,
PRIMARY KEY (ID),
KEY NAME (NAME)
);
SELECT DISTINCT
t2.id AS key_link_id,
t2.name AS link
FROM t1
LEFT JOIN t2 ON t1.link_id=t2.id
GROUP BY t1.id
ORDER BY link;
key_link_id	link
NULL	NULL
drop table t1,t2;
create table t1 (
id		int not null,
name	tinytext not null,
unique	(id)
);
create table t2 (
id		int not null,
idx		int not null,
unique	(id, idx)
);
create table t3 (
id		int not null,
idx		int not null,
unique	(id, idx)
);
insert into t1 values (1,'yes'), (2,'no');
insert into t2 values (1,1);
insert into t3 values (1,1);
EXPLAIN
SELECT DISTINCT
t1.id
from
t1
straight_join
t2
straight_join
t3
straight_join
t1 as j_lj_t2 left join t2 as t2_lj
on j_lj_t2.id=t2_lj.id
straight_join
t1 as j_lj_t3 left join t3 as t3_lj
on j_lj_t3.id=t3_lj.id
WHERE
((t1.id=j_lj_t2.id AND t2_lj.id IS NULL) OR (t1.id=t2.id AND t2.idx=2))
AND ((t1.id=j_lj_t3.id AND t3_lj.id IS NULL) OR (t1.id=t3.id AND t3.idx=2));
table	type	possible_keys	key	key_len	ref	rows	Extra
t1	index	id	id	4	NULL	2	Using index; Using temporary
t2	index	id	id	8	NULL	1	Using index; Distinct
t3	index	id	id	8	NULL	1	Using index; Distinct
j_lj_t2	index	id	id	4	NULL	2	where used; Using index; Distinct
t2_lj	index	id	id	8	NULL	1	where used; Using index; Distinct
j_lj_t3	index	id	id	4	NULL	2	where used; Using index; Distinct
t3_lj	index	id	id	8	NULL	1	where used; Using index; Distinct
SELECT DISTINCT
t1.id
from
t1
straight_join
t2
straight_join
t3
straight_join
t1 as j_lj_t2 left join t2 as t2_lj
on j_lj_t2.id=t2_lj.id
straight_join
t1 as j_lj_t3 left join t3 as t3_lj
on j_lj_t3.id=t3_lj.id
WHERE
((t1.id=j_lj_t2.id AND t2_lj.id IS NULL) OR (t1.id=t2.id AND t2.idx=2))
AND ((t1.id=j_lj_t3.id AND t3_lj.id IS NULL) OR (t1.id=t3.id AND t3.idx=2));
id
2
drop table t1,t2,t3;
drop table if exists t1;
create table t1 (a int not null, b int not null, t time);
insert into t1 values (1,1,"00:06:15"),(1,2,"00:06:15"),(1,2,"00:30:15"),(1,3,"00:06:15"),(1,3,"00:30:15");
select a,sec_to_time(sum(time_to_sec(t))) from t1 group by a,b;
a	sec_to_time(sum(time_to_sec(t)))
1	00:06:15
1	00:36:30
1	00:36:30
select distinct a,sec_to_time(sum(time_to_sec(t))) from t1 group by a,b;
a	sec_to_time(sum(time_to_sec(t)))
1	00:06:15
1	00:36:30
create table t2 (a int not null primary key, b int);
insert into t2 values (1,1),(2,2),(3,3);
select t1.a,sec_to_time(sum(time_to_sec(t))) from t1 left join t2 on (t1.b=t2.a) group by t1.a,t2.b;
a	sec_to_time(sum(time_to_sec(t)))
1	00:06:15
1	00:36:30
1	00:36:30
select distinct t1.a,sec_to_time(sum(time_to_sec(t))) from t1 left join t2 on (t1.b=t2.a) group by t1.a,t2.b;
a	sec_to_time(sum(time_to_sec(t)))
1	00:06:15
1	00:36:30
drop table t1,t2;
create table t1 (a int not null,b char(5), c text);
insert into t1 (a) values (1),(2),(3),(4),(1),(2),(3),(4);
select distinct a from t1 group by b,a having a > 2 order by a desc;
a
4
3
select distinct a,c from t1 group by b,c,a having a > 2 order by a desc;
a	c
4	NULL
3	NULL
drop table t1;