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(*) NULL 1 0 6 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),(3,1),(4,1); 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; id select_type table type possible_keys key key_len ref rows Extra 1 SIMPLE t1 ALL PRIMARY NULL NULL NULL 4 Using temporary 1 SIMPLE t3 ref a a 5 test.t1.b 2 Using where; Using index 1 SIMPLE t2 index a a 4 NULL 5 Using where; Using index; Distinct; Using join buffer 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; id select_type table type possible_keys key key_len ref rows Extra 1 SIMPLE t1 index PRIMARY PRIMARY 4 NULL 4 Using index; Using temporary 1 SIMPLE t3 ref a a 5 test.t1.a 11 Using where; 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 explain SELECT distinct t1.a from t1; id select_type table type possible_keys key key_len ref rows Extra 1 SIMPLE t1 index NULL PRIMARY 4 NULL 4 Using index explain SELECT distinct t1.a from t1 order by a desc; id select_type table type possible_keys key key_len ref rows Extra 1 SIMPLE t1 index NULL PRIMARY 4 NULL 4 Using index explain SELECT t1.a from t1 group by a order by a desc; id select_type table type possible_keys key key_len ref rows Extra 1 SIMPLE t1 index NULL PRIMARY 4 NULL 4 Using index explain SELECT distinct t1.a from t1 order by a desc limit 1; id select_type table type possible_keys key key_len ref rows Extra 1 SIMPLE t1 index NULL PRIMARY 4 NULL 1 Using index explain SELECT distinct a from t3 order by a desc limit 2; id select_type table type possible_keys key key_len ref rows Extra 1 SIMPLE t3 index NULL a 5 NULL 40 Using index explain SELECT distinct a,b from t3 order by a+1; id select_type table type possible_keys key key_len ref rows Extra 1 SIMPLE t3 ALL NULL NULL NULL NULL 204 Using temporary; Using filesort explain SELECT distinct a,b from t3 order by a limit 2; id select_type table type possible_keys key key_len ref rows Extra 1 SIMPLE t3 index NULL a 5 NULL 2 Using temporary explain SELECT a,b from t3 group by a,b order by a+1; id select_type table type possible_keys key key_len ref rows Extra 1 SIMPLE t3 ALL NULL NULL NULL NULL 204 Using temporary; Using filesort 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)); id select_type table type possible_keys key key_len ref rows Extra 1 SIMPLE t1 index id id 4 NULL 2 Using index; Using temporary 1 SIMPLE t2 index id id 8 NULL 1 Using index; Distinct; Using join buffer 1 SIMPLE t3 index id id 8 NULL 1 Using index; Distinct; Using join buffer 1 SIMPLE j_lj_t2 index id id 4 NULL 2 Using where; Using index; Distinct; Using join buffer 1 SIMPLE t2_lj ref id id 4 test.j_lj_t2.id 1 Using where; Using index; Distinct 1 SIMPLE j_lj_t3 index id id 4 NULL 2 Using where; Using index; Distinct; Using join buffer 1 SIMPLE t3_lj ref id id 4 test.j_lj_t3.id 1 Using where; 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; 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; create table t1 (a char(1), key(a)) engine=myisam; insert into t1 values('1'),('1'); select * from t1 where a >= '1'; a 1 1 select distinct a from t1 order by a desc; a 1 select distinct a from t1 where a >= '1' order by a desc; a 1 drop table t1; CREATE TABLE t1 (email varchar(50), infoID BIGINT, dateentered DATETIME); CREATE TABLE t2 (infoID BIGINT, shipcode varchar(10)); INSERT INTO t1 (email, infoID, dateentered) VALUES ('test1@testdomain.com', 1, '2002-07-30 22:56:38'), ('test1@testdomain.com', 1, '2002-07-27 22:58:16'), ('test2@testdomain.com', 1, '2002-06-19 15:22:19'), ('test2@testdomain.com', 2, '2002-06-18 14:23:47'), ('test3@testdomain.com', 1, '2002-05-19 22:17:32'); INSERT INTO t2(infoID, shipcode) VALUES (1, 'Z001'), (2, 'R002'); SELECT DISTINCTROW email, shipcode FROM t1, t2 WHERE t1.infoID=t2.infoID; email shipcode test1@testdomain.com Z001 test2@testdomain.com Z001 test2@testdomain.com R002 test3@testdomain.com Z001 SELECT DISTINCTROW email FROM t1 ORDER BY dateentered DESC; email test1@testdomain.com test2@testdomain.com test3@testdomain.com SELECT DISTINCTROW email, shipcode FROM t1, t2 WHERE t1.infoID=t2.infoID ORDER BY dateentered DESC; email shipcode test1@testdomain.com Z001 test2@testdomain.com Z001 test2@testdomain.com R002 test3@testdomain.com Z001 drop table t1,t2; CREATE TABLE t1 (privatemessageid int(10) unsigned NOT NULL auto_increment, folderid smallint(6) NOT NULL default '0', userid int(10) unsigned NOT NULL default '0', touserid int(10) unsigned NOT NULL default '0', fromuserid int(10) unsigned NOT NULL default '0', title varchar(250) NOT NULL default '', message mediumtext NOT NULL, dateline int(10) unsigned NOT NULL default '0', showsignature smallint(6) NOT NULL default '0', iconid smallint(5) unsigned NOT NULL default '0', messageread smallint(6) NOT NULL default '0', readtime int(10) unsigned NOT NULL default '0', receipt smallint(6) unsigned NOT NULL default '0', deleteprompt smallint(6) unsigned NOT NULL default '0', multiplerecipients smallint(6) unsigned NOT NULL default '0', PRIMARY KEY (privatemessageid), KEY userid (userid)) ENGINE=MyISAM; INSERT INTO t1 VALUES (128,0,33,33,8,':D','',996121863,1,0,2,996122850,2,0,0); CREATE TABLE t2 (userid int(10) unsigned NOT NULL auto_increment, usergroupid smallint(5) unsigned NOT NULL default '0', username varchar(50) NOT NULL default '', password varchar(50) NOT NULL default '', email varchar(50) NOT NULL default '', styleid smallint(5) unsigned NOT NULL default '0', parentemail varchar(50) NOT NULL default '', coppauser smallint(6) NOT NULL default '0', homepage varchar(100) NOT NULL default '', icq varchar(20) NOT NULL default '', aim varchar(20) NOT NULL default '', yahoo varchar(20) NOT NULL default '', signature mediumtext NOT NULL, adminemail smallint(6) NOT NULL default '0', showemail smallint(6) NOT NULL default '0', invisible smallint(6) NOT NULL default '0', usertitle varchar(250) NOT NULL default '', customtitle smallint(6) NOT NULL default '0', joindate int(10) unsigned NOT NULL default '0', cookieuser smallint(6) NOT NULL default '0', daysprune smallint(6) NOT NULL default '0', lastvisit int(10) unsigned NOT NULL default '0', lastactivity int(10) unsigned NOT NULL default '0', lastpost int(10) unsigned NOT NULL default '0', posts smallint(5) unsigned NOT NULL default '0', timezoneoffset varchar(4) NOT NULL default '', emailnotification smallint(6) NOT NULL default '0', buddylist mediumtext NOT NULL, ignorelist mediumtext NOT NULL, pmfolders mediumtext NOT NULL, receivepm smallint(6) NOT NULL default '0', emailonpm smallint(6) NOT NULL default '0', pmpopup smallint(6) NOT NULL default '0', avatarid smallint(6) NOT NULL default '0', avatarrevision int(6) unsigned NOT NULL default '0', options smallint(6) NOT NULL default '15', birthday date NOT NULL default '0000-00-00', maxposts smallint(6) NOT NULL default '-1', startofweek smallint(6) NOT NULL default '1', ipaddress varchar(20) NOT NULL default '', referrerid int(10) unsigned NOT NULL default '0', nosessionhash smallint(6) NOT NULL default '0', autorefresh smallint(6) NOT NULL default '-1', messagepopup tinyint(2) NOT NULL default '0', inforum smallint(5) unsigned NOT NULL default '0', ratenum smallint(5) unsigned NOT NULL default '0', ratetotal smallint(5) unsigned NOT NULL default '0', allowrate smallint(5) unsigned NOT NULL default '1', PRIMARY KEY (userid), KEY usergroupid (usergroupid), KEY username (username), KEY inforum (inforum)) ENGINE=MyISAM; INSERT INTO t2 VALUES (33,6,'Kevin','0','kevin@stileproject.com',1,'',0,'http://www.stileproject.com','','','','',1,1,0,'Administrator',0,996120694,1,-1,1030996168,1031027028,1030599436,36,'-6',0,'','','',1,0,1,0,0,15,'0000-00-00',-1,1,'64.0.0.0',0,1,-1,0,0,4,19,1); SELECT DISTINCT t1.*, t2.* FROM t1 LEFT JOIN t2 ON (t2.userid = t1.touserid); privatemessageid folderid userid touserid fromuserid title message dateline showsignature iconid messageread readtime receipt deleteprompt multiplerecipients userid usergroupid username password email styleid parentemail coppauser homepage icq aim yahoo signature adminemail showemail invisible usertitle customtitle joindate cookieuser daysprune lastvisit lastactivity lastpost posts timezoneoffset emailnotification buddylist ignorelist pmfolders receivepm emailonpm pmpopup avatarid avatarrevision options birthday maxposts startofweek ipaddress referrerid nosessionhash autorefresh messagepopup inforum ratenum ratetotal allowrate 128 0 33 33 8 :D 996121863 1 0 2 996122850 2 0 0 33 6 Kevin 0 kevin@stileproject.com 1 0 http://www.stileproject.com 1 1 0 Administrator 0 996120694 1 -1 1030996168 1031027028 1030599436 36 -6 0 1 0 1 0 0 15 0000-00-00 -1 1 64.0.0.0 0 1 -1 0 0 4 19 1 DROP TABLE t1,t2; CREATE TABLE t1 (a int primary key, b int, c int); INSERT t1 VALUES (1,2,3); CREATE TABLE t2 (a int primary key, b int, c int); INSERT t2 VALUES (3,4,5); SELECT DISTINCT t1.a, t2.b FROM t1, t2 WHERE t1.a=1 ORDER BY t2.c; a b 1 4 DROP TABLE t1,t2; CREATE table t1 ( `id` int(11) NOT NULL auto_increment, `name` varchar(50) NOT NULL default '', PRIMARY KEY (`id`)) ENGINE=MyISAM AUTO_INCREMENT=3 ; INSERT INTO t1 VALUES (1, 'aaaaa'); INSERT INTO t1 VALUES (3, 'aaaaa'); INSERT INTO t1 VALUES (2, 'eeeeeee'); select distinct left(name,1) as name from t1; name a e 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); INSERT INTO t1 (ID, NAME, LINK_ID) VALUES (2,'Jack',0); INSERT INTO t1 (ID, NAME, LINK_ID) VALUES (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 ( html varchar(5) default NULL, rin int(11) default '0', rout int(11) default '0' ) ENGINE=MyISAM; INSERT INTO t1 VALUES ('1',1,0); SELECT DISTINCT html,SUM(rout)/(SUM(rin)+1) as 'prod' FROM t1 GROUP BY rin; html prod 1 0.0000 drop table t1; CREATE TABLE t1 (a int); INSERT INTO t1 VALUES (1),(2),(3),(4),(5); SELECT DISTINCT a, 1 FROM t1; a 1 1 1 2 1 3 1 4 1 5 1 SELECT DISTINCT 1, a FROM t1; 1 a 1 1 1 2 1 3 1 4 1 5 CREATE TABLE t2 (a int, b int); INSERT INTO t2 VALUES (1,1),(2,2),(2,3),(2,4),(3,5); SELECT DISTINCT a, b, 2 FROM t2; a b 2 1 1 2 2 2 2 2 3 2 2 4 2 3 5 2 SELECT DISTINCT 2, a, b FROM t2; 2 a b 2 1 1 2 2 2 2 2 3 2 2 4 2 3 5 SELECT DISTINCT a, 2, b FROM t2; a 2 b 1 2 1 2 2 2 2 2 3 2 2 4 3 2 5 DROP TABLE t1,t2; CREATE TABLE t1(a INT PRIMARY KEY, b INT); INSERT INTO t1 VALUES (1,1), (2,1), (3,1); EXPLAIN SELECT DISTINCT a FROM t1; id select_type table type possible_keys key key_len ref rows Extra 1 SIMPLE t1 index NULL PRIMARY 4 NULL 3 Using index EXPLAIN SELECT DISTINCT a,b FROM t1; id select_type table type possible_keys key key_len ref rows Extra 1 SIMPLE t1 ALL NULL NULL NULL NULL 3 EXPLAIN SELECT DISTINCT t1_1.a, t1_1.b FROM t1 t1_1, t1 t1_2; id select_type table type possible_keys key key_len ref rows Extra 1 SIMPLE t1_1 ALL NULL NULL NULL NULL 3 Using temporary 1 SIMPLE t1_2 index NULL PRIMARY 4 NULL 3 Using index; Distinct; Using join buffer EXPLAIN SELECT DISTINCT t1_1.a, t1_1.b FROM t1 t1_1, t1 t1_2 WHERE t1_1.a = t1_2.a; id select_type table type possible_keys key key_len ref rows Extra 1 SIMPLE t1_1 ALL PRIMARY NULL NULL NULL 3 Using temporary 1 SIMPLE t1_2 eq_ref PRIMARY PRIMARY 4 test.t1_1.a 1 Using index; Distinct EXPLAIN SELECT a FROM t1 GROUP BY a; id select_type table type possible_keys key key_len ref rows Extra 1 SIMPLE t1 index NULL PRIMARY 4 NULL 3 Using index EXPLAIN SELECT a,b FROM t1 GROUP BY a,b; id select_type table type possible_keys key key_len ref rows Extra 1 SIMPLE t1 ALL NULL NULL NULL NULL 3 Using filesort EXPLAIN SELECT DISTINCT a,b FROM t1 GROUP BY a,b; id select_type table type possible_keys key key_len ref rows Extra 1 SIMPLE t1 ALL NULL NULL NULL NULL 3 Using filesort CREATE TABLE t2(a INT, b INT NOT NULL, c INT NOT NULL, d INT, PRIMARY KEY (a,b)); INSERT INTO t2 VALUES (1,1,1,50), (1,2,3,40), (2,1,3,4); EXPLAIN SELECT DISTINCT a FROM t2; id select_type table type possible_keys key key_len ref rows Extra 1 SIMPLE t2 index NULL PRIMARY 8 NULL 3 Using index EXPLAIN SELECT DISTINCT a,a FROM t2; id select_type table type possible_keys key key_len ref rows Extra 1 SIMPLE t2 index NULL PRIMARY 8 NULL 3 Using index EXPLAIN SELECT DISTINCT b,a FROM t2; id select_type table type possible_keys key key_len ref rows Extra 1 SIMPLE t2 index NULL PRIMARY 8 NULL 3 Using index EXPLAIN SELECT DISTINCT a,c FROM t2; id select_type table type possible_keys key key_len ref rows Extra 1 SIMPLE t2 ALL NULL NULL NULL NULL 3 Using temporary EXPLAIN SELECT DISTINCT c,a,b FROM t2; id select_type table type possible_keys key key_len ref rows Extra 1 SIMPLE t2 ALL NULL NULL NULL NULL 3 EXPLAIN SELECT DISTINCT a,b,d FROM t2 GROUP BY c,b,d; id select_type table type possible_keys key key_len ref rows Extra 1 SIMPLE t2 ALL NULL NULL NULL NULL 3 Using temporary; Using filesort CREATE UNIQUE INDEX c_b_unq ON t2 (c,b); EXPLAIN SELECT DISTINCT a,b,d FROM t2 GROUP BY c,b,d; id select_type table type possible_keys key key_len ref rows Extra 1 SIMPLE t2 ALL NULL NULL NULL NULL 3 Using filesort DROP TABLE t1,t2; create table t1 (id int, dsc varchar(50)); insert into t1 values (1, "line number one"), (2, "line number two"), (3, "line number three"); select distinct id, IFNULL(dsc, '-') from t1; id IFNULL(dsc, '-') 1 line number one 2 line number two 3 line number three drop table t1; CREATE TABLE t1 (a int primary key, b int); INSERT INTO t1 (a,b) values (1,1), (2,3), (3,2); explain SELECT DISTINCT a, b FROM t1 ORDER BY b; id select_type table type possible_keys key key_len ref rows Extra 1 SIMPLE t1 ALL NULL NULL NULL NULL 3 Using filesort SELECT DISTINCT a, b FROM t1 ORDER BY b; a b 1 1 3 2 2 3 DROP TABLE t1; CREATE TABLE t1 ( ID int(11) NOT NULL auto_increment, x varchar(20) default NULL, y decimal(10,0) default NULL, PRIMARY KEY (ID), KEY (y) ) ENGINE=MyISAM DEFAULT CHARSET=latin1; INSERT INTO t1 VALUES (1,'ba','-1'), (2,'ba','1150'), (306,'ba','-1'), (307,'ba','1150'), (611,'ba','-1'), (612,'ba','1150'); select count(distinct x,y) from t1; count(distinct x,y) 2 select count(distinct concat(x,y)) from t1; count(distinct concat(x,y)) 2 drop table t1; CREATE TABLE t1 (a INT, b INT, PRIMARY KEY (a,b)); INSERT INTO t1 VALUES (1, 101); INSERT INTO t1 SELECT a + 1, a + 101 FROM t1; INSERT INTO t1 SELECT a + 2, a + 102 FROM t1; INSERT INTO t1 SELECT a + 4, a + 104 FROM t1; INSERT INTO t1 SELECT a + 8, a + 108 FROM t1; EXPLAIN SELECT DISTINCT a,a FROM t1 WHERE b < 12 ORDER BY a; id select_type table type possible_keys key key_len ref rows Extra 1 SIMPLE t1 index NULL PRIMARY 8 NULL 16 Using where; Using index SELECT DISTINCT a,a FROM t1 WHERE b < 12 ORDER BY a; a a DROP TABLE t1; DROP TABLE IF EXISTS t1; CREATE TABLE t1 (id INT NOT NULL, fruit_id INT NOT NULL, fruit_name varchar(20) default NULL); INSERT INTO t1 VALUES (1,1,'ORANGE'); INSERT INTO t1 VALUES (2,2,'APPLE'); INSERT INTO t1 VALUES (3,2,'APPLE'); INSERT INTO t1 VALUES (4,3,'PEAR'); SELECT DISTINCT fruit_id, fruit_name INTO @v1, @v2 FROM t1 WHERE fruit_name = 'APPLE'; SELECT @v1, @v2; @v1 @v2 2 APPLE SELECT DISTINCT fruit_id, fruit_name INTO @v3, @v4 FROM t1 GROUP BY fruit_id, fruit_name HAVING fruit_name = 'APPLE'; SELECT @v3, @v4; @v3 @v4 2 APPLE SELECT DISTINCT @v5:= fruit_id, @v6:= fruit_name INTO @v7, @v8 FROM t1 WHERE fruit_name = 'APPLE'; SELECT @v5, @v6, @v7, @v8; @v5 @v6 @v7 @v8 2 APPLE 2 APPLE SELECT DISTINCT @v5 + fruit_id, CONCAT(@v6, fruit_name) INTO @v9, @v10 FROM t1 WHERE fruit_name = 'APPLE'; SELECT @v5, @v6, @v7, @v8, @v9, @v10; @v5 @v6 @v7 @v8 @v9 @v10 2 APPLE 2 APPLE 4 APPLEAPPLE SELECT DISTINCT @v11:= @v5 + fruit_id, @v12:= CONCAT(@v6, fruit_name) INTO @v13, @v14 FROM t1 WHERE fruit_name = 'APPLE'; SELECT @v11, @v12, @v13, @v14; @v11 @v12 @v13 @v14 4 APPLEAPPLE 4 APPLEAPPLE SELECT DISTINCT @v13, @v14 INTO @v15, @v16 FROM t1 WHERE fruit_name = 'APPLE'; SELECT @v15, @v16; @v15 @v16 4 APPLEAPPLE SELECT DISTINCT 2 + 2, 'Bob' INTO @v17, @v18 FROM t1 WHERE fruit_name = 'APPLE'; SELECT @v17, @v18; @v17 @v18 4 Bob DROP TABLE IF EXISTS t2; CREATE TABLE t2 (fruit_id INT NOT NULL, fruit_name varchar(20) default NULL); SELECT DISTINCT fruit_id, fruit_name INTO OUTFILE '../../tmp/data1.tmp' FROM t1 WHERE fruit_name = 'APPLE'; LOAD DATA INFILE '../../tmp/data1.tmp' INTO TABLE t2; SELECT DISTINCT @v19:= fruit_id, @v20:= fruit_name INTO OUTFILE '../../tmp/data2.tmp' FROM t1 WHERE fruit_name = 'APPLE'; LOAD DATA INFILE '../../tmp/data2.tmp' INTO TABLE t2; SELECT @v19, @v20; @v19 @v20 2 APPLE SELECT * FROM t2; fruit_id fruit_name 2 APPLE 2 APPLE DROP TABLE t1; DROP TABLE t2; CREATE TABLE t1 (a CHAR(1)); INSERT INTO t1 VALUES('A'), (0); SELECT a FROM t1 WHERE a=0; a A 0 Warnings: Warning 1292 Truncated incorrect DOUBLE value: 'A' SELECT DISTINCT a FROM t1 WHERE a=0; a A 0 Warnings: Warning 1292 Truncated incorrect DOUBLE value: 'A' DROP TABLE t1; CREATE TABLE t1 (a DATE); INSERT INTO t1 VALUES ('1972-07-29'), ('1972-02-06'); EXPLAIN SELECT (SELECT DISTINCT a FROM t1 WHERE a = '2002-08-03'); id select_type table type possible_keys key key_len ref rows Extra 1 PRIMARY NULL NULL NULL NULL NULL NULL NULL No tables used 2 SUBQUERY t1 ALL NULL NULL NULL NULL 2 Using where EXPLAIN SELECT (SELECT DISTINCT ADDDATE(a,1) FROM t1 WHERE ADDDATE(a,1) = '2002-08-03'); id select_type table type possible_keys key key_len ref rows Extra 1 PRIMARY NULL NULL NULL NULL NULL NULL NULL No tables used 2 SUBQUERY t1 ALL NULL NULL NULL NULL 2 Using where CREATE TABLE t2 (a CHAR(5) CHARACTER SET latin1 COLLATE latin1_general_ci); INSERT INTO t2 VALUES (0xf6); INSERT INTO t2 VALUES ('oe'); SELECT COUNT(*) FROM (SELECT DISTINCT a FROM t2) dt; COUNT(*) 2 SELECT COUNT(*) FROM (SELECT DISTINCT a FROM t2 WHERE a='oe' COLLATE latin1_german2_ci) dt; COUNT(*) 2 DROP TABLE t1, t2; CREATE TABLE t1 (a INT, UNIQUE (a)); INSERT INTO t1 VALUES (4),(null),(2),(1),(null),(3); EXPLAIN SELECT DISTINCT a FROM t1; id select_type table type possible_keys key key_len ref rows Extra 1 SIMPLE t1 index NULL a 5 NULL 6 Using index SELECT DISTINCT a FROM t1; a NULL 1 2 3 4 EXPLAIN SELECT a FROM t1 GROUP BY a; id select_type table type possible_keys key key_len ref rows Extra 1 SIMPLE t1 index NULL a 5 NULL 6 Using index SELECT a FROM t1 GROUP BY a; a NULL 1 2 3 4 DROP TABLE t1; CREATE TABLE t1 (a INT, b INT); INSERT INTO t1 VALUES(1,1),(1,2),(1,3); SELECT DISTINCT a, b FROM t1; a b 1 1 1 2 1 3 SELECT DISTINCT a, a, b FROM t1; a a b 1 1 1 1 1 2 1 1 3 DROP TABLE t1; End of 5.0 tests CREATE TABLE t1(a INT, b INT, c INT, d INT, e INT, PRIMARY KEY(a,b,c,d,e), KEY(a,b,d,c) ); INSERT INTO t1(a, b, c) VALUES (1, 1, 1), (1, 1, 2), (1, 1, 3), (1, 2, 1), (1, 2, 2), (1, 2, 3); EXPLAIN SELECT DISTINCT a, b, d, c FROM t1; id select_type table type possible_keys key key_len ref rows Extra 1 SIMPLE t1 range NULL PRIMARY 16 NULL 7 Using index for group-by; Using temporary SELECT DISTINCT a, b, d, c FROM t1; a b d c 1 1 0 1 1 1 0 2 1 1 0 3 1 2 0 1 1 2 0 2 1 2 0 3 DROP TABLE t1; # # Bug #46159: simple query that never returns # SET @old_max_heap_table_size = @@max_heap_table_size; SET @@max_heap_table_size = 16384; SET @old_sort_buffer_size = @@sort_buffer_size; SET @@sort_buffer_size = 32804; CREATE TABLE t1(c1 int, c2 VARCHAR(20)); INSERT INTO t1 VALUES (1, '1'), (1, '1'), (2, '2'), (3, '1'), (3, '1'), (4, '4'); INSERT INTO t1 SELECT 5 + 10000 * RAND(), '5' FROM t1; INSERT INTO t1 SELECT 5 + 10000 * RAND(), '5' FROM t1; INSERT INTO t1 SELECT 5 + 10000 * RAND(), '5' FROM t1; INSERT INTO t1 SELECT 5 + 10000 * RAND(), '5' FROM t1; INSERT INTO t1 SELECT 5 + 10000 * RAND(), '5' FROM t1; INSERT INTO t1 SELECT 5 + 10000 * RAND(), '5' FROM t1; INSERT INTO t1 SELECT 5 + 10000 * RAND(), '5' FROM t1; INSERT INTO t1 SELECT 5 + 10000 * RAND(), '5' FROM t1; SELECT c1, c2, COUNT(*) FROM t1 GROUP BY c1 LIMIT 4; c1 c2 COUNT(*) 1 1 2 2 2 1 3 1 2 4 4 1 SELECT DISTINCT c2 FROM t1 GROUP BY c1 HAVING COUNT(*) > 1; c2 1 5 DROP TABLE t1; SET @@sort_buffer_size = @old_sort_buffer_size; SET @@max_heap_table_size = @old_max_heap_table_size; End of 5.1 tests