drop table if exists t1,t2,t3; SET SQL_WARNINGS=1; CREATE TABLE t1 ( ID CHAR(32) NOT NULL, name CHAR(32) NOT NULL, value CHAR(255), INDEX indexIDname (ID(8),name(8)) ) ; INSERT INTO t1 VALUES ('keyword','indexdir','/export/home/local/www/database/indexes/keyword'); INSERT INTO t1 VALUES ('keyword','urlprefix','text/ /text'); INSERT INTO t1 VALUES ('keyword','urlmap','/text/ /'); INSERT INTO t1 VALUES ('keyword','attr','personal employee company'); INSERT INTO t1 VALUES ('emailgids','indexdir','/export/home/local/www/database/indexes/emailgids'); INSERT INTO t1 VALUES ('emailgids','urlprefix','text/ /text'); INSERT INTO t1 VALUES ('emailgids','urlmap','/text/ /'); INSERT INTO t1 VALUES ('emailgids','attr','personal employee company'); SELECT value FROM t1 WHERE ID='emailgids' AND name='attr'; value personal employee company drop table t1; CREATE TABLE t1 ( price int(5) DEFAULT '0' NOT NULL, area varchar(40) DEFAULT '' NOT NULL, type varchar(40) DEFAULT '' NOT NULL, transityes enum('Y','N') DEFAULT 'Y' NOT NULL, shopsyes enum('Y','N') DEFAULT 'Y' NOT NULL, schoolsyes enum('Y','N') DEFAULT 'Y' NOT NULL, petsyes enum('Y','N') DEFAULT 'Y' NOT NULL, KEY price (price,area,type,transityes,shopsyes,schoolsyes,petsyes) ); INSERT INTO t1 VALUES (900,'Vancouver','Shared/Roomate','N','N','N','N'); INSERT INTO t1 VALUES (900,'Vancouver','Shared/Roomate','N','N','N','N'); INSERT IGNORE INTO t1 VALUES (900,'Vancouver','Shared/Roomate','','','',''); Warnings: Warning 1265 Data truncated for column 'transityes' at row 1 Warning 1265 Data truncated for column 'shopsyes' at row 1 Warning 1265 Data truncated for column 'schoolsyes' at row 1 Warning 1265 Data truncated for column 'petsyes' at row 1 INSERT INTO t1 VALUES (900,'Vancouver','Shared/Roomate','Y','Y','Y','Y'); INSERT INTO t1 VALUES (900,'Vancouver','Shared/Roomate','Y','Y','Y','Y'); INSERT INTO t1 VALUES (900,'Vancouver','Shared/Roomate','Y','Y','Y','Y'); INSERT INTO t1 VALUES (900,'Vancouver','Shared/Roomate','Y','Y','Y','Y'); INSERT INTO t1 VALUES (900,'Vancouver','Shared/Roomate','Y','Y','Y','Y'); SELECT * FROM t1 WHERE area='Vancouver' and transityes='y' and schoolsyes='y' and ( ((type='1 Bedroom' or type='Studio/Bach') and (price<=500)) or ((type='2 Bedroom') and (price<=550)) or ((type='Shared/Roomate') and (price<=300)) or ((type='Room and Board') and (price<=500)) ) and price <= 400; price area type transityes shopsyes schoolsyes petsyes drop table t1; CREATE TABLE t1 (program enum('signup','unique','sliding') not null, type enum('basic','sliding','signup'), sites set('mt'), PRIMARY KEY (program)); ALTER TABLE t1 modify program enum('signup','unique','sliding'); drop table t1; CREATE TABLE t1 ( name varchar(50) DEFAULT '' NOT NULL, author varchar(50) DEFAULT '' NOT NULL, category decimal(10,0) DEFAULT '0' NOT NULL, email varchar(50), password varchar(50), proxy varchar(50), bitmap varchar(20), msg varchar(255), urlscol varchar(127), urlhttp varchar(127), timeout decimal(10,0), nbcnx decimal(10,0), creation decimal(10,0), livinguntil decimal(10,0), lang decimal(10,0), type decimal(10,0), subcat decimal(10,0), subtype decimal(10,0), reg char(1), scs varchar(255), capacity decimal(10,0), userISP varchar(50), CCident varchar(50) DEFAULT '' NOT NULL, PRIMARY KEY (name,author,category) ); INSERT INTO t1 VALUES ('patnom','patauteur',0,'p.favre@cryo-networks.fr',NULL,NULL,'#p2sndnq6ae5g1u6t','essai salut','scol://195.242.78.119:patauteur.patnom',NULL,NULL,NULL,950036174,-882087474,NULL,3,0,3,'1','Pub/patnom/futur_divers.scs',NULL,'pat','CC1'); INSERT INTO t1 VALUES ('LeNomDeMonSite','Marc',0,'m.barilley@cryo-networks.fr',NULL,NULL,NULL,NULL,'scol://195.242.78.119:Marc.LeNomDeMonSite',NULL,NULL,NULL,950560434,-881563214,NULL,3,0,3,'1','Pub/LeNomDeMonSite/domus_hibere.scs',NULL,'Marq','CC1'); select * from t1 where name='patnom' and author='patauteur' and category=0; name author category email password proxy bitmap msg urlscol urlhttp timeout nbcnx creation livinguntil lang type subcat subtype reg scs capacity userISP CCident patnom patauteur 0 p.favre@cryo-networks.fr NULL NULL #p2sndnq6ae5g1u6t essai salut scol://195.242.78.119:patauteur.patnom NULL NULL NULL 950036174 -882087474 NULL 3 0 3 1 Pub/patnom/futur_divers.scs NULL pat CC1 drop table t1; create table t1 ( name_id int not null auto_increment, name blob, INDEX name_idx (name(5)), primary key (name_id) ); INSERT t1 VALUES(NULL,'/'); INSERT t1 VALUES(NULL,'[T,U]_axpby'); SELECT * FROM t1 WHERE name='[T,U]_axpy'; name_id name SELECT * FROM t1 WHERE name='[T,U]_axpby'; name_id name 2 [T,U]_axpby create table t2 ( name_id int not null auto_increment, name char(255) binary, INDEX name_idx (name(5)), primary key (name_id) ); INSERT t2 select * from t1; SELECT * FROM t2 WHERE name='[T,U]_axpy'; name_id name SELECT * FROM t2 WHERE name='[T,U]_axpby'; name_id name 2 [T,U]_axpby CREATE TABLE t3 SELECT * FROM t2 WHERE name='[T,U]_axpby'; SELECT * FROM t2 WHERE name='[T,U]_axpby'; name_id name 2 [T,U]_axpby drop table t1,t2,t3; create table t1 ( SEQNO numeric(12 ) not null, MOTYPEID numeric(12 ) not null, MOINSTANCEID numeric(12 ) not null, ATTRID numeric(12 ) not null, VALUE varchar(120) not null, primary key (SEQNO, MOTYPEID, MOINSTANCEID, ATTRID, VALUE ) ); INSERT INTO t1 VALUES (1, 1, 1, 1, 'a'); INSERT INTO t1 VALUES (1, 1, 1, 1, 'b'); INSERT INTO t1 VALUES (1, 1, 1, 1, 'a'); ERROR 23000: Duplicate entry '1-1-1-1-a' for key 'PRIMARY' drop table t1; CREATE TABLE t1 ( a tinytext NOT NULL, b tinyint(3) unsigned NOT NULL default '0', PRIMARY KEY (a(32),b) ) ENGINE=MyISAM; INSERT INTO t1 VALUES ('a',1),('a',2); SELECT * FROM t1 WHERE a='a' AND b=2; a b a 2 SELECT * FROM t1 WHERE a='a' AND b in (2); a b a 2 SELECT * FROM t1 WHERE a='a' AND b in (1,2); a b a 1 a 2 drop table t1; create table t1 (a int not null unique, b int unique, c int, d int not null primary key, key(c), e int not null unique); show keys from t1; Table Non_unique Key_name Seq_in_index Column_name Collation Cardinality Sub_part Packed Null Index_type Comment Index_comment t1 0 PRIMARY 1 d A 0 NULL NULL BTREE t1 0 a 1 a A 0 NULL NULL BTREE t1 0 e 1 e A 0 NULL NULL BTREE t1 0 b 1 b A NULL NULL NULL YES BTREE t1 1 c 1 c A NULL NULL NULL YES BTREE drop table t1; CREATE TABLE t1 (c CHAR(10) NOT NULL,i INT NOT NULL AUTO_INCREMENT, UNIQUE (c,i)); INSERT IGNORE INTO t1 (c) VALUES (NULL),(NULL); Warnings: Warning 1048 Column 'c' cannot be null Warning 1048 Column 'c' cannot be null SELECT * FROM t1; c i 1 2 INSERT INTO t1 (c) VALUES ('a'),('a'); SELECT * FROM t1; c i 1 2 a 1 a 2 DROP TABLE IF EXISTS t1; CREATE TABLE t1 (c CHAR(10) NULL, i INT NOT NULL AUTO_INCREMENT, UNIQUE (c,i)); INSERT INTO t1 (c) VALUES (NULL),(NULL); SELECT * FROM t1; c i NULL 1 NULL 2 INSERT INTO t1 (c) VALUES ('a'),('a'); SELECT * FROM t1; c i NULL 1 NULL 2 a 1 a 2 drop table t1; create table t1 (i int, a char(200), b text, unique (a), unique (b(300))) charset utf8; insert ignore t1 values (1, repeat('a',210), repeat('b', 310)); Warnings: Warning 1265 Data truncated for column 'a' at row 1 insert ignore t1 values (2, repeat(0xD0B1,215), repeat(0xD0B1, 310)); Warnings: Warning 1265 Data truncated for column 'a' at row 1 select i, length(a), length(b), char_length(a), char_length(b) from t1; i length(a) length(b) char_length(a) char_length(b) 1 200 310 200 310 2 400 620 200 310 select i from t1 where a=repeat(_utf8 'a',200); i 1 select i from t1 where a=repeat(_utf8 0xD0B1,200); i 2 select i from t1 where b=repeat(_utf8 'b',310); i 1 drop table t1; CREATE TABLE t1 (id int unsigned auto_increment, name char(50), primary key (id)) engine=myisam; insert into t1 (name) values ('a'), ('b'),('c'),('d'),('e'),('f'),('g'); explain select 1 from t1 where id =2; id select_type table type possible_keys key key_len ref rows Extra 1 SIMPLE t1 const PRIMARY PRIMARY 4 const 1 Using index explain select 1 from t1 where id =2 or id=3; id select_type table type possible_keys key key_len ref rows Extra 1 SIMPLE t1 index PRIMARY PRIMARY 4 NULL 7 Using where; Using index explain select name from t1 where id =2; id select_type table type possible_keys key key_len ref rows Extra 1 SIMPLE t1 const PRIMARY PRIMARY 4 const 1 ALTER TABLE t1 DROP PRIMARY KEY, ADD INDEX (id); explain select 1 from t1 where id =2; id select_type table type possible_keys key key_len ref rows Extra 1 SIMPLE t1 ref id id 4 const 1 Using index drop table t1; CREATE TABLE t1 (numeropost mediumint(8) unsigned NOT NULL default '0', numreponse int(10) unsigned NOT NULL auto_increment, PRIMARY KEY (numeropost,numreponse), UNIQUE KEY numreponse (numreponse)); INSERT INTO t1 (numeropost,numreponse) VALUES ('1','1'),('1','2'),('2','3'),('2','4'); SELECT numeropost FROM t1 WHERE numreponse='1'; numeropost 1 EXPLAIN SELECT numeropost FROM t1 WHERE numreponse='1'; id select_type table type possible_keys key key_len ref rows Extra 1 SIMPLE t1 const numreponse numreponse 4 const 1 Using index FLUSH TABLES; SELECT numeropost FROM t1 WHERE numreponse='1'; numeropost 1 drop table t1; create table t1 (c varchar(30) character set utf8, t text character set utf8, unique (c(2)), unique (t(3))) engine=myisam; show create table t1; Table Create Table t1 CREATE TABLE `t1` ( `c` varchar(30) CHARACTER SET utf8 DEFAULT NULL, `t` text CHARACTER SET utf8 DEFAULT NULL, UNIQUE KEY `c` (`c`(2)), UNIQUE KEY `t` (`t`(3)) ) ENGINE=MyISAM DEFAULT CHARSET=latin1 insert t1 values ('cccc', 'tttt'), (0xD0B1212223D0B1D0B1D0B1D0B1D0B1, 0xD0B1D0B1212223D0B1D0B1D0B1D0B1), (0xD0B1222123D0B1D0B1D0B1D0B1D0B1, 0xD0B1D0B1222123D0B1D0B1D0B1D0B1); insert t1 (c) values ('cc22'); ERROR 23000: Duplicate entry 'cc' for key 'c' insert t1 (t) values ('ttt22'); ERROR 23000: Duplicate entry 'ttt' for key 't' insert t1 (c) values (0xD0B1212322D0B1D0B1D0B1D0B1D0B1); ERROR 23000: Duplicate entry '\0431!' for key 'c' insert t1 (t) values (0xD0B1D0B1212322D0B1D0B1D0B1D0B1); ERROR 23000: Duplicate entry '\0431\0431!' for key 't' select c from t1 where c='cccc'; c cccc select t from t1 where t='tttt'; t tttt select c from t1 where c=0xD0B1212223D0B1D0B1D0B1D0B1D0B1; c ?!"#????? select t from t1 where t=0xD0B1D0B1212223D0B1D0B1D0B1D0B1; t ??!"#???? drop table t1; DROP TABLE IF EXISTS t1; Warnings: Note 1051 Unknown table 'test.t1' CREATE TABLE t1 ( c1 int, c2 varbinary(240), UNIQUE KEY (c1), KEY (c2) ) ENGINE=MyISAM; INSERT INTO t1 VALUES (1,'\Z\Z\Z\Z'); INSERT INTO t1 VALUES (2,'\Z\Z\Z\Z\Z\Z'); INSERT INTO t1 VALUES (3,'\Z\Z\Z\Z'); select c1 from t1 where c2='\Z\Z\Z\Z'; c1 1 3 DELETE FROM t1 WHERE (c1 = 1); check table t1; Table Op Msg_type Msg_text test.t1 check status OK select c1 from t1 where c2='\Z\Z\Z\Z'; c1 3 DELETE FROM t1 WHERE (c1 = 3); check table t1; Table Op Msg_type Msg_text test.t1 check status OK select c1 from t1 where c2='\Z\Z\Z\Z'; c1 truncate table t1; insert into t1 values(1,"aaaa"),(2,"aaab"),(3,"aaac"),(4,"aaccc"); delete from t1 where c1=3; delete from t1 where c1=1; delete from t1 where c1=4; check table t1; Table Op Msg_type Msg_text test.t1 check status OK drop table t1; create table t1 (c char(10), index (c(0))); ERROR HY000: Key part 'c' length cannot be 0 create table t1 (c char(10), index (c,c)); ERROR 42S21: Duplicate column name 'c' create table t1 (c1 char(10), c2 char(10), index (c1,c2,c1)); ERROR 42S21: Duplicate column name 'c1' create table t1 (c1 char(10), c2 char(10), index (c1,c1,c2)); ERROR 42S21: Duplicate column name 'c1' create table t1 (c1 char(10), c2 char(10), index (c2,c1,c1)); ERROR 42S21: Duplicate column name 'c1' create table t1 (c1 char(10), c2 char(10)); alter table t1 add key (c1,c1); ERROR 42S21: Duplicate column name 'c1' alter table t1 add key (c2,c1,c1); ERROR 42S21: Duplicate column name 'c1' alter table t1 add key (c1,c2,c1); ERROR 42S21: Duplicate column name 'c1' alter table t1 add key (c1,c1,c2); ERROR 42S21: Duplicate column name 'c1' drop table t1; create table t1 ( i1 INT NOT NULL, i2 INT NOT NULL, UNIQUE i1idx (i1), UNIQUE i2idx (i2)); desc t1; Field Type Null Key Default Extra i1 int(11) NO PRI NULL i2 int(11) NO UNI NULL show create table t1; Table Create Table t1 CREATE TABLE `t1` ( `i1` int(11) NOT NULL, `i2` int(11) NOT NULL, UNIQUE KEY `i1idx` (`i1`), UNIQUE KEY `i2idx` (`i2`) ) ENGINE=MyISAM DEFAULT CHARSET=latin1 drop table t1; create table t1 ( c1 int, c2 varchar(20) not null, primary key (c1), key (c2(10)) ) engine=myisam; insert into t1 values (1,''); insert into t1 values (2,' \t\tTest String'); insert into t1 values (3,' \n\tTest String'); update t1 set c2 = 'New Test String' where c1 = 1; select * from t1; c1 c2 1 New Test String 2 Test String 3 Test String drop table t1; create table t1 (a varchar(10), b varchar(10), key(a(10),b(10))); show create table t1; Table Create Table t1 CREATE TABLE `t1` ( `a` varchar(10) DEFAULT NULL, `b` varchar(10) DEFAULT NULL, KEY `a` (`a`,`b`) ) ENGINE=MyISAM DEFAULT CHARSET=latin1 alter table t1 modify b varchar(20); show create table t1; Table Create Table t1 CREATE TABLE `t1` ( `a` varchar(10) DEFAULT NULL, `b` varchar(20) DEFAULT NULL, KEY `a` (`a`,`b`) ) ENGINE=MyISAM DEFAULT CHARSET=latin1 alter table t1 modify a varchar(20); show create table t1; Table Create Table t1 CREATE TABLE `t1` ( `a` varchar(20) DEFAULT NULL, `b` varchar(20) DEFAULT NULL, KEY `a` (`a`,`b`) ) ENGINE=MyISAM DEFAULT CHARSET=latin1 drop table t1; create table t1 (a int not null primary key, b varchar(20) not null unique); desc t1; Field Type Null Key Default Extra a int(11) NO PRI NULL b varchar(20) NO UNI NULL drop table t1; create table t1 (a int not null primary key, b int not null unique); desc t1; Field Type Null Key Default Extra a int(11) NO PRI NULL b int(11) NO UNI NULL drop table t1; create table t1 (a int not null primary key, b varchar(20) not null, unique (b(10))); desc t1; Field Type Null Key Default Extra a int(11) NO PRI NULL b varchar(20) NO UNI NULL drop table t1; create table t1 (a int not null primary key, b varchar(20) not null, c varchar(20) not null, unique(b(10),c(10))); desc t1; Field Type Null Key Default Extra a int(11) NO PRI NULL b varchar(20) NO MUL NULL c varchar(20) NO NULL drop table t1; create table t1 ( c1 int, c2 char(12), c3 varchar(123), c4 timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP, index (c1), index i1 (c1), index i2 (c2), index i3 (c3), unique i4 (c4), index i5 (c1, c2, c3, c4), primary key (c2, c3), index (c2, c4)); Warnings: Note 1831 Duplicate index `i1`. This is deprecated and will be disallowed in a future release show create table t1; Table Create Table t1 CREATE TABLE `t1` ( `c1` int(11) DEFAULT NULL, `c2` char(12) NOT NULL, `c3` varchar(123) NOT NULL, `c4` timestamp NOT NULL DEFAULT current_timestamp() ON UPDATE current_timestamp(), PRIMARY KEY (`c2`,`c3`), UNIQUE KEY `i4` (`c4`), KEY `c1` (`c1`), KEY `i1` (`c1`), KEY `i2` (`c2`), KEY `i3` (`c3`), KEY `i5` (`c1`,`c2`,`c3`,`c4`), KEY `c2` (`c2`,`c4`) ) ENGINE=MyISAM DEFAULT CHARSET=latin1 alter table t1 drop index c1; alter table t1 add index (c1); Warnings: Note 1831 Duplicate index `c1`. This is deprecated and will be disallowed in a future release alter table t1 add index (c1); Warnings: Note 1831 Duplicate index `c1_2`. This is deprecated and will be disallowed in a future release alter table t1 drop index i3; alter table t1 add index i3 (c3); alter table t1 drop index i2, drop index i4; alter table t1 add index i2 (c2), add index i4 (c4); alter table t1 drop index i2, drop index i4, add index i6 (c2, c4); Warnings: Note 1831 Duplicate index `i6`. This is deprecated and will be disallowed in a future release alter table t1 add index i2 (c2), add index i4 (c4), drop index i6; alter table t1 drop index i2, drop index i4, add unique i4 (c4); alter table t1 add index i2 (c2), drop index i4, add index i4 (c4); alter table t1 drop index c2, add index (c2(4),c3(7)); alter table t1 drop index c2, add index (c2(4),c3(7)); alter table t1 add primary key (c1, c2), drop primary key; alter table t1 drop primary key; alter table t1 add primary key (c1, c2), drop primary key; ERROR 42000: Can't DROP INDEX `PRIMARY`; check that it exists show create table t1; Table Create Table t1 CREATE TABLE `t1` ( `c1` int(11) NOT NULL, `c2` char(12) NOT NULL, `c3` varchar(123) NOT NULL, `c4` timestamp NOT NULL DEFAULT current_timestamp() ON UPDATE current_timestamp(), KEY `i1` (`c1`), KEY `i5` (`c1`,`c2`,`c3`,`c4`), KEY `c1` (`c1`), KEY `c1_2` (`c1`), KEY `i3` (`c3`), KEY `i2` (`c2`), KEY `i4` (`c4`), KEY `c2` (`c2`(4),`c3`(7)) ) ENGINE=MyISAM DEFAULT CHARSET=latin1 insert into t1 values(1, 'a', 'a', NULL); insert into t1 values(1, 'b', 'b', NULL); alter table t1 drop index i3, drop index i2, drop index i1; alter table t1 add index i3 (c3), add index i2 (c2), add unique index i1 (c1); ERROR 23000: Duplicate entry '1' for key 'i1' drop table t1; CREATE TABLE t1( a TINYINT, KEY(a) ) ENGINE=MyISAM; INSERT INTO t1 VALUES( 1 ); ALTER TABLE t1 DISABLE KEYS; EXPLAIN SELECT MAX(a) FROM t1 FORCE INDEX(a); id select_type table type possible_keys key key_len ref rows Extra 1 SIMPLE t1 system NULL NULL NULL NULL 1 drop table t1; CREATE TABLE t1 ( a INTEGER auto_increment PRIMARY KEY, b INTEGER NOT NULL, c INTEGER NOT NULL, d CHAR(64) ); CREATE TABLE t2 ( a INTEGER auto_increment PRIMARY KEY, b INTEGER NOT NULL, c SMALLINT NOT NULL, d DATETIME NOT NULL, e SMALLINT NOT NULL, f INTEGER NOT NULL, g INTEGER NOT NULL, h SMALLINT NOT NULL, i INTEGER NOT NULL, j INTEGER NOT NULL, UNIQUE INDEX (b), INDEX (b, d, e, f, g, h, i, j, c), INDEX (c) ); INSERT INTO t2 VALUES (NULL, 1, 254, '1000-01-01 00:00:00', 257, 0, 0, 0, 0, 0), (NULL, 2, 1, '2004-11-30 12:00:00', 1, 0, 0, 0, 0, 0), (NULL, 3, 1, '2004-11-30 12:00:00', 1, 0, 0, 2, -21600, 0), (NULL, 4, 1, '2004-11-30 12:00:00', 1, 0, 0, 2, -10800, 0), (NULL, 5, 1, '2004-11-30 12:00:00', 1, 0, 0, 5, -10800, 0), (NULL, 6, 1, '2004-11-30 12:00:00', 102, 0, 0, 0, 0, 0), (NULL, 7, 1, '2004-11-30 12:00:00', 105, 2, 0, 0, 0, 0), (NULL, 8, 1, '2004-11-30 12:00:00', 105, 10, 0, 0, 0, 0); INSERT INTO t1 (b, c, d) VALUES (3388000, -553000, NULL), (3388000, -553000, NULL); SELECT * FROM t2 c JOIN t1 pa ON c.b = pa.a WHERE c.c = 1 ORDER BY c.b, c.d ; a b c d e f g h i j a b c d 2 2 1 2004-11-30 12:00:00 1 0 0 0 0 0 2 3388000 -553000 NULL DROP TABLE t1, t2; create table t1(a int not null, key aa(a), b char(10) not null, unique key bb(b(1)), c char(4) not null, unique key cc(c)); desc t1; Field Type Null Key Default Extra a int(11) NO MUL NULL b char(10) NO UNI NULL c char(4) NO PRI NULL show create table t1; Table Create Table t1 CREATE TABLE `t1` ( `a` int(11) NOT NULL, `b` char(10) NOT NULL, `c` char(4) NOT NULL, UNIQUE KEY `cc` (`c`), UNIQUE KEY `bb` (`b`(1)), KEY `aa` (`a`) ) ENGINE=MyISAM DEFAULT CHARSET=latin1 drop table t1; create table t1(a int not null, key aa(a), b char(10) not null, unique key bb(b(1)), c char(4) not null); desc t1; Field Type Null Key Default Extra a int(11) NO MUL NULL b char(10) NO UNI NULL c char(4) NO NULL alter table t1 add unique key cc(c); desc t1; Field Type Null Key Default Extra a int(11) NO MUL NULL b char(10) NO UNI NULL c char(4) NO PRI NULL show create table t1; Table Create Table t1 CREATE TABLE `t1` ( `a` int(11) NOT NULL, `b` char(10) NOT NULL, `c` char(4) NOT NULL, UNIQUE KEY `cc` (`c`), UNIQUE KEY `bb` (`b`(1)), KEY `aa` (`a`) ) ENGINE=MyISAM DEFAULT CHARSET=latin1 drop table t1; End of 5.0 tests DROP TABLE IF EXISTS t1; CREATE TABLE t1 (a INT PRIMARY KEY AUTO_INCREMENT); INSERT INTO t1 VALUES (), (), (); SELECT 1 AS c1 FROM t1 ORDER BY ( SELECT 1 AS c2 FROM t1 GROUP BY GREATEST(LAST_INSERT_ID(), t1.a) ASC LIMIT 1); c1 1 1 1 DROP TABLE t1; CREATE TABLE t1 (a INT, b INT, INDEX (a,b)); INSERT INTO t1 (a, b) VALUES (1,1), (1,2), (1,3), (1,4), (1,5), (2,2), (2,3), (2,1), (3,1), (4,1), (4,2), (4,3), (4,4), (4,5), (4,6); EXPLAIN SELECT 1 FROM t1 AS t1_outer WHERE (SELECT max(b) FROM t1 GROUP BY a HAVING a < 2) > 12; id select_type table type possible_keys key key_len ref rows Extra 1 PRIMARY NULL NULL NULL NULL NULL NULL NULL Impossible WHERE 2 SUBQUERY t1 range NULL a 5 NULL 8 Using index for group-by SELECT 1 as RES FROM t1 AS t1_outer WHERE (SELECT max(b) FROM t1 GROUP BY a HAVING a < 2) > 12; RES DROP TABLE t1; # # Bug#18144: Cost with FORCE/USE index seems incorrect in some cases. # # We are interested in showing that the cost for the last plan is higher # than for the preceding two plans. # CREATE TABLE t1( a INT, b INT, KEY( a ) ); INSERT INTO t1 values (1, 2), (1, 3), (2, 3), (2, 4), (3, 4), (3, 5); EXPLAIN SELECT a, SUM( b ) FROM t1 GROUP BY a; id select_type table type possible_keys key key_len ref rows Extra 1 SIMPLE t1 ALL NULL NULL NULL NULL 6 Using temporary; Using filesort SHOW STATUS LIKE 'Last_query_cost'; Variable_name Value Last_query_cost 9.212184 EXPLAIN SELECT a, SUM( b ) FROM t1 USE INDEX( a ) GROUP BY a; id select_type table type possible_keys key key_len ref rows Extra 1 SIMPLE t1 ALL NULL NULL NULL NULL 6 Using temporary; Using filesort SHOW STATUS LIKE 'Last_query_cost'; Variable_name Value Last_query_cost 9.212184 EXPLAIN SELECT a, SUM( b ) FROM t1 FORCE INDEX( a ) 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 SHOW STATUS LIKE 'Last_query_cost'; Variable_name Value Last_query_cost 14.199000 DROP TABLE t1;