一.索引：索引是表的目录，在查找内容之前可以先在目录中查找索引位置，以此快速定位查询数据。对于索引，会保存在额外的文件中 1.1. 创建一个索引: mysql> create index ix_class on tb3(class_id); Query OK, 0 rows affected (0.02 sec) Records: 0 Duplicates: 0 Warnings: 0 1.2. 删除一个索引: mysql> drop index ix_class on tb3; Query OK, 0 rows affected (0.02 sec) Records: 0 Duplicates: 0 Warnings: 0二 . 索引种类1.普通索引 --- 加速查找mysql> show databases;+--------------------+| Database |+--------------------+| db1 || information_schema || mysql || performance_schema || sys |+--------------------+5 rows in set (0.02 sec) mysql> use db1; Database changed mysql> create table t11( -> nid int not null auto_increment primary key, -> name varchar(255), -> emile varchar(255))engine=innodb default charset=utf8; Query OK, 0 rows affected, 1 warning (0.03 sec) mysql> create index ix_name on t11(name); Query OK, 0 rows affected (0.02 sec) Records: 0 Duplicates: 0 Warnings: 0 mysql> show index from t11; +-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+---------+------------+ | Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment | Visible | Expression | +-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+---------+------------+ | t11 | 0 | PRIMARY | 1 | nid | A | 0 | NULL | NULL | | BTREE | | | YES | NULL | | t11 | 1 | ix_name | 1 | name | A | 0 | NULL | NULL | YES | BTREE | | | YES | NULL | +-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+---------+------------+2 rows in set (0.01 sec)2.唯一索引 --- 加速查找，约束列数据不能重复，可以为nullcreate unique index ix_name on t11(name);3.主键索引 --- 加速查找，约束列数据不能重复，不能为null mysql> create table tb3( -> nid int not null auto_increment, -> class_id varchar(255), -> name varchar(255), -> unique ix_name (name), -> primary key(nid))engine=innodb default charset='utf8'; Query OK, 0 rows affected, 1 warning (0.03 sec)4.组合索引 --- 多列可以创建一个索引文件 <1>普通组合索引: 无约束 <2>联合组合索引: 有约束，两列数据同时不相同时才可以插入，否则报错 组合索引遵循最左匹配原则 三.覆盖索引 与 合并索引 1.覆盖索引 如果情况应用上索引，不用去数据表中操作 ---- 覆盖索引 即只需要在索引表中就能获取数据 而: select * from t1 where nid = 1; (1)要先去索引中找 (2)再去数据表中找 2.合并索引 nid name(单独索引) email(单独索引) select name from t1 where name='star'; select name from t1 where email='486075@qq.com'; select name from t1 where name='xiaozhang' or email='486075@qq.com'; 判断业务需求，选择合并索引 还是 组合索引 三.mysql执行计划 mysql> select * from tb1; +-----+------------+ | nid | class | +-----+------------+ | 1 | 三年级二班 | | 2 | 五年级 | +-----+------------+1. explain sql语句1.1. ALL --- 全表扫描，对于数据表从头到尾找一遍 mysql> explain select * from student; +----+-------------+---------+------------+------+---------------+------+---------+------+------+----------+-------+ | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | +----+-------------+---------+------------+------+---------------+------+---------+------+------+----------+-------+ | 1 | SIMPLE | student | NULL | ALL | NULL | NULL | NULL | NULL | 26 | 100.00 | NULL | +----+-------------+---------+------------+------+---------------+------+---------+------+------+----------+-------+ 如果type值是ALL --- 表示要对数据表进行全部扫描1.2 index --- 全索引扫描，对索引从头到尾找一遍 mysql> explain select class from tb1; +----+-------------+-------+------------+-------+---------------+----------+---------+------+------+----------+-------------+ | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | +----+-------------+-------+------------+-------+---------------+----------+---------+------+------+----------+-------------+ | 1 | SIMPLE | tb1 | NULL | index | NULL | ix_class | 1022 | NULL | 2 | 100.00 | Using index | +----+-------------+-------+------------+-------+---------------+----------+---------+------+------+----------+-------------+ 如果type值是index --- 表示要对索引表进行全部扫描 ALL 和 index 这两种的执行效率不高 1.1.limit 如果加上limit： 特别的：如果有limit限制，则找到之后就不在继续向下扫描 select sname from student where sname='沙比'; select sname from student where sname='沙比' limit 1; 虽然上述两个语句都会进行全表扫描，第二句使用了limit，则找到一个后就不再继续扫描1.3.range --- 对索引列进行范围查找对索引列进行范围查找，要注意，如果条件为 > != 的情况下，不能应用到索引 1.3.1 mysql> explain select sname from student where sname<'张'; +----+-------------+---------+------------+-------+---------------+-------+---------+------+------+----------+--------------------------+ | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | +----+-------------+---------+------------+-------+---------------+-------+---------+------+------+----------+--------------------------+ | 1 | SIMPLE | student | NULL | range | ix_sn | ix_sn | 98 | NULL | 11 | 100.00 | Using where; Using index | +----+-------------+---------+------------+-------+---------------+-------+---------+------+------+----------+--------------------------+1.4 index_merge --- 合并索引，使用多个单列索引搜索 mysql> explain select * from student where sid=5 or sname='刘二'; +----+-------------+---------+------------+-------------+---------------+---------------+---------+------+------+----------+-----------------------------------------+ | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | +----+-------------+---------+------------+-------------+---------------+---------------+---------+------+------+----------+-----------------------------------------+ | 1 | SIMPLE | student | NULL | index_merge | PRIMARY,ix_sn | PRIMARY,ix_sn | 4,98 | NULL | 2 | 100.00 | Using union(PRIMARY,ix_sn); Using where | +----+-------------+---------+------------+-------------+---------------+---------------+---------+------+------+----------+-----------------------------------------+1 row in set, 1 warning (0.00 sec)1.5 ref ---根据索引查找一个或多个值 eg: mysql> explain select * from student where sname='star'; +----+-------------+---------+------------+------+---------------+-------+---------+-------+------+----------+-------+ | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | +----+-------------+---------+------------+------+---------------+-------+---------+-------+------+----------+-------+ | 1 | SIMPLE | student | NULL | ref | ix_sn | ix_sn | 98 | const | 3 | 100.00 | NULL | +----+-------------+---------+------------+------+---------------+-------+---------+-------+------+----------+-------+1 row in set, 1 warning (0.00 sec)1.6 eq_ref --- 连接时使用primary key 或 unique类型 eg:
mysql> explain select student.class_id,class.caption from student left join class on student.sid=class.cid where student.class_id=1 and class.caption='队长';
+----+-------------+---------+------------+--------+------------------+---------+---------+---------------+------+----------+-------------+
| id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra |
+----+-------------+---------+------------+--------+------------------+---------+---------+---------------+------+----------+-------------+
| 1 | SIMPLE | class | NULL | ALL | PRIMARY | NULL | NULL | NULL | 8 | 12.50 | Using where |
| 1 | SIMPLE | student | NULL | eq_ref | PRIMARY,fk_class | PRIMARY | 4 | db1.class.cid | 1 | 34.62 | Using where |
+----+-------------+---------+------------+--------+------------------+---------+---------+---------------+------+----------+-------------+
1.7 const ---表最多有一个匹配行,因为仅有一行,在这行的列值可被优化器剩余部分认为是常数, const表很快,因为它们只读取一次。 mysql> explain select sid from student where sid=8; +----+-------------+---------+------------+-------+---------------+---------+---------+-------+------+----------+-------------+ | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | +----+-------------+---------+------------+-------+---------------+---------+---------+-------+------+----------+-------------+ | 1 | SIMPLE | student | NULL | const | PRIMARY | PRIMARY | 4 | const | 1 | 100.00 | Using index | +----+-------------+---------+------------+-------+---------------+---------+---------+-------+------+----------+-------------+1.8 system ---系统 表仅有一行(为系统表)-----这是const联接类型的一个特例。 possible_keys ------可能使用的索引 key ----真实使用的 key_len --------mysql中使用索引字节长度四.正确使用索引1.用like的时候，% 在前不走索引 mysql> explain select * from student where sname like '%三'; +----+-------------+---------+------------+------+---------------+------+---------+------+------+----------+-------------+ | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | +----+-------------+---------+------------+------+---------------+------+---------+------+------+----------+-------------+ | 1 | SIMPLE | student | NULL | ALL | NULL | NULL | NULL | NULL | 26 | 11.11 | Using where | +----+-------------+---------+------------+------+---------------+------+---------+------+------+----------+-------------+ 1 row in set, 1 warning (0.00 sec) mysql> explain select * from student where sname like '三%'; +----+-------------+---------+------------+-------+---------------+-------+---------+------+------+----------+-----------------------+ | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | +----+-------------+---------+------------+-------+---------------+-------+---------+------+------+----------+-----------------------+ | 1 | SIMPLE | student | NULL | range | ix_sn | ix_sn | 98 | NULL | 1 | 100.00 | Using index condition | +----+-------------+---------+------------+-------+---------------+-------+---------+------+------+----------+-----------------------+ 1 row in set, 1 warning (0.00 sec)2.sql语句中加函数不走索引 mysql> explain select * from student where substring(sname,1,4)='star'; +----+-------------+---------+------------+------+---------------+------+---------+------+------+----------+-------------+ | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | +----+-------------+---------+------------+------+---------------+------+---------+------+------+----------+-------------+ | 1 | SIMPLE | student | NULL | ALL | NULL | NULL | NULL | NULL | 26 | 100.00 | Using where | +----+-------------+---------+------------+------+---------------+------+---------+------+------+----------+-------------+ 1 row in set, 1 warning (0.00 sec)3.数据类型不一致，也会造成不走索引 mysql> explain select * from student where sname='star'; +----+-------------+---------+------------+------+---------------+-------+---------+-------+------+----------+-------+ | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | +----+-------------+---------+------------+------+---------------+-------+---------+-------+------+----------+-------+ | 1 | SIMPLE | student | NULL | ref | ix_sn | ix_sn | 98 | const | 3 | 100.00 | NULL | +----+-------------+---------+------------+------+---------------+-------+---------+-------+------+----------+-------+ 1 row in set, 1 warning (0.00 sec) mysql> explain select * from student where sname=555; +----+-------------+---------+------------+------+---------------+------+---------+------+------+----------+-------------+ | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | +----+-------------+---------+------------+------+---------------+------+---------+------+------+----------+-------------+ | 1 | SIMPLE | student | NULL | ALL | ix_sn | NULL | NULL | NULL | 26 | 10.00 | Using where | +----+-------------+---------+------------+------+---------------+------+---------+------+------+----------+-------------+ 1 row in set, 3 warnings (0.00 sec)4. 条件是 != 与 > ，走不走索引 4.1-----如果是普通索引，!=的话，不走索引 eg: mysql> explain select * from student where sname!='star'; +----+-------------+---------+------------+------+---------------+------+---------+------+------+----------+-------------+ | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | +----+-------------+---------+------------+------+---------------+------+---------+------+------+----------+-------------+ | 1 | SIMPLE | student | NULL | ALL | ix_sn | NULL | NULL | NULL | 26 | 96.15 | Using where | +----+-------------+---------+------------+------+---------------+------+---------+------+------+----------+-------------+ 1 row in set, 1 warning (0.00 sec) 4.2 mysql> desc tb3; +----------+--------------+------+-----+---------+----------------+ | Field | Type | Null | Key | Default | Extra | +----------+--------------+------+-----+---------+----------------+ | nid | int | NO | PRI | NULL | auto_increment | | class_id | varchar(255) | YES | | NULL | | | name | varchar(255) | YES | UNI | NULL | | +----------+--------------+------+-----+---------+----------------+ 3 rows in set (0.00 sec) 4.2.1 -----如果是唯一索引，!=的话，走索引 eg: mysql> explain select * from tb3 where name!='star'; +----+-------------+-------+------------+-------+---------------+---------+---------+------+------+----------+-----------------------+ | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | +----+-------------+-------+------------+-------+---------------+---------+---------+------+------+----------+-----------------------+ | 1 | SIMPLE | tb3 | NULL | range | ix_name | ix_name | 768 | NULL | 2 | 100.00 | Using index condition | +----+-------------+-------+------------+-------+---------------+---------+---------+------+------+----------+-----------------------+ 1 row in set, 1 warning (0.00 sec) 4.2.2 -----如果是主键索引，!=的话，走索引 mysql> explain select * from tb3 where nid!=8; +----+-------------+-------+------------+-------+---------------+---------+---------+------+------+----------+-------------+ | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | +----+-------------+-------+------------+-------+---------------+---------+---------+------+------+----------+-------------+ | 1 | SIMPLE | tb3 | NULL | range | PRIMARY | PRIMARY | 4 | NULL | 2 | 100.00 | Using where | +----+-------------+-------+------------+-------+---------------+---------+---------+------+------+----------+-------------+ 1 row in set, 1 warning (0.00 sec) 4.2.3 ----索引是整数类型还是会走索引 4.2.4 -----如果是主键索引，> 的话，走索引 eg: mysql> explain select * from tb3 where nid>8; +----+-------------+-------+------------+-------+---------------+---------+---------+------+------+----------+-------------+ | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | +----+-------------+-------+------------+-------+---------------+---------+---------+------+------+----------+-------------+ | 1 | SIMPLE | tb3 | NULL | range | PRIMARY | PRIMARY | 4 | NULL | 1 | 100.00 | Using where | +----+-------------+-------+------------+-------+---------------+---------+---------+------+------+----------+-------------+ 1 row in set, 1 warning (0.00 sec) result:如果是主键索引，> 的话，走索引 4.2.5 -----如果是唯一索引，> 的话，走索引 eg: mysql> explain select name from tb3 where name>'star'; +----+-------------+-------+------------+-------+---------------+---------+---------+------+------+----------+--------------------------+ | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | +----+-------------+-------+------------+-------+---------------+---------+---------+------+------+----------+--------------------------+ | 1 | SIMPLE | tb3 | NULL | index | ix_name | ix_name | 768 | NULL | 1 | 100.00 | Using where; Using index | +----+-------------+-------+------------+-------+---------------+---------+---------+------+------+----------+--------------------------+ 1 row in set, 1 warning (0.00 sec) result: 如果是唯一索引，> 的话，走索引 4.2.6.1 ----索引是整数类型，> 还是会走索引 # 给表tb3 添加一列 num ,且num为整型类型 mysql> alter table tb3 add num int; Query OK, 0 rows affected (0.01 sec) Records: 0 Duplicates: 0 Warnings: 0 mysql> desc tb3; +----------+--------------+------+-----+---------+----------------+ | Field | Type | Null | Key | Default | Extra | +----------+--------------+------+-----+---------+----------------+ | nid | int | NO | PRI | NULL | auto_increment | | class_id | varchar(255) | YES | | NULL | | | name | varchar(255) | YES | UNI | NULL | | | num | int | YES | | NULL | | +----------+--------------+------+-----+---------+----------------+ 给列 num 添加索引 mysql> create index ix_num on tb3(num); Query OK, 0 rows affected (0.01 sec) Records: 0 Duplicates: 0 Warnings: 0 eg: mysql> explain select num from tb3 where num>15; +----+-------------+-------+------------+-------+---------------+--------+---------+------+------+----------+--------------------------+ | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | +----+-------------+-------+------------+-------+---------------+--------+---------+------+------+----------+--------------------------+ | 1 | SIMPLE | tb3 | NULL | index | ix_num | ix_num | 5 | NULL | 1 | 100.00 | Using where; Using index | +----+-------------+-------+------------+-------+---------------+--------+---------+------+------+----------+--------------------------+ result: 索引是整数类型，> 还是会走索引 4.2.6.2 ---- ----索引是整数类型，!=还是会走索引 mysql> explain select num from tb3 where num!=15; +----+-------------+-------+------------+-------+---------------+--------+---------+------+------+----------+--------------------------+ | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | +----+-------------+-------+------------+-------+---------------+--------+---------+------+------+----------+--------------------------+ | 1 | SIMPLE | tb3 | NULL | index | ix_num | ix_num | 5 | NULL | 1 | 100.00 | Using where; Using index | +----+-------------+-------+------------+-------+---------------+--------+---------+------+------+----------+--------------------------+ 1 row in set, 1 warning (0.00 sec) 4 rows in set (0.00 sec) result:索引是整数类型，!=还是会走索引 4.2.7 -----如果是普通索引，>的话，不走索引 如下，给tb3表新添加一列 parient 数据类型为 varchar mysql> alter table tb3 add parient varchar(255); Query OK, 0 rows affected (0.02 sec) Records: 0 Duplicates: 0 Warnings: 0 mysql> show index from tb3; +-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+---------+------------+ | Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment | Visible | Expression | +-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+---------+------------+ | tb3 | 0 | PRIMARY | 1 | nid | A | 0 | NULL | NULL | | BTREE | | | YES | NULL | | tb3 | 0 | ix_name | 1 | name | A | 0 | NULL | NULL | YES | BTREE | | | YES | NULL | | tb3 | 1 | ix_num | 1 | num | A | 0 | NULL | NULL | YES | BTREE | | | YES | NULL | +-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+---------+------------+ 3 rows in set (0.00 sec) mysql> desc tb3; +----------+--------------+------+-----+---------+----------------+ | Field | Type | Null | Key | Default | Extra | +----------+--------------+------+-----+---------+----------------+ | nid | int | NO | PRI | NULL | auto_increment | | class_id | varchar(255) | YES | | NULL | | | name | varchar(255) | YES | UNI | NULL | | | num | int | YES | MUL | NULL | | | parient | varchar(255) | YES | | NULL | | +----------+--------------+------+-----+---------+----------------+ 5 rows in set (0.00 sec) parient 为普通列 mysql> explain select parient from tb3 where parient>'star'; +----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+-------------+ | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | +----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+-------------+ | 1 | SIMPLE | tb3 | NULL | ALL | NULL | NULL | NULL | NULL | 1 | 100.00 | Using where | +----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+-------------+ 1 row in set, 1 warning (0.00 sec) result: 如果是普通索引，> 的话，不走索引,type 为ALL5.条件里有order by 走不走所引 mysql> explain select * from tb3 order by name desc; +----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+----------------+ | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | +----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+----------------+ | 1 | SIMPLE | tb3 | NULL | ALL | NULL | NULL | NULL | NULL | 1 | 100.00 | Using filesort | +----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+----------------+ 1 row in set, 1 warning (0.00 sec) 结论:不走索引 mysql> explain select name from tb3 order by name desc; +----+-------------+-------+------------+-------+---------------+---------+---------+------+------+----------+----------------------------------+ | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | +----+-------------+-------+------------+-------+---------------+---------+---------+------+------+----------+----------------------------------+ | 1 | SIMPLE | tb3 | NULL | index | NULL | ix_name | 768 | NULL | 1 | 100.00 | Backward index scan; Using index | +----+-------------+-------+------------+-------+---------------+---------+---------+------+------+----------+----------------------------------+ 1 row in set, 1 warning (0.00 sec) 结论:走索引 对于主键nid，* mysql> explain select * from tb3 order by nid desc; +----+-------------+-------+------------+-------+---------------+---------+---------+------+------+----------+---------------------+ | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | +----+-------------+-------+------------+-------+---------------+---------+---------+------+------+----------+---------------------+ | 1 | SIMPLE | tb3 | NULL | index | NULL | PRIMARY | 4 | NULL | 1 | 100.00 | Backward index scan | +----+-------------+-------+------------+-------+---------------+---------+---------+------+------+----------+---------------------+ 1 row in set, 1 warning (0.00 sec) 结论:走索引6.如果是三个列组成联合索引 --给tb3添加两列 child mom mysql> desc tb3; +----------+--------------+------+-----+---------+----------------+ | Field | Type | Null | Key | Default | Extra | +----------+--------------+------+-----+---------+----------------+ | nid | int | NO | PRI | NULL | auto_increment | | class_id | varchar(255) | YES | | NULL | | | name | varchar(255) | YES | UNI | NULL | | | num | int | YES | MUL | NULL | | | parient | varchar(255) | YES | | NULL | | | child | varchar(255) | YES | | NULL | | | mom | varchar(255) | YES | | NULL | | +----------+--------------+------+-----+---------+----------------+ 给 parient child mom 创建组合索引: 如下: mysql> create index ix_pa_ch_mo on tb3(parient,child,mom); Query OK, 0 rows affected (0.02 sec) Records: 0 Duplicates: 0 Warnings: 0 mysql> desc tb3; +----------+--------------+------+-----+---------+----------------+ | Field | Type | Null | Key | Default | Extra | +----------+--------------+------+-----+---------+----------------+ | nid | int | NO | PRI | NULL | auto_increment | | class_id | varchar(255) | YES | | NULL | | | name | varchar(255) | YES | UNI | NULL | | | num | int | YES | MUL | NULL | | | parient | varchar(255) | YES | MUL | NULL | | | child | varchar(255) | YES | | NULL | | | mom | varchar(255) | YES | | NULL | | +----------+--------------+------+-----+---------+----------------+ 7 rows in set (0.00 sec) question:查找组合索引后面两个列时，是不是走索引 mysql> explain select child,mom from tb3 where child='star' and mom='mother'; +----+-------------+-------+------------+-------+---------------+-------------+---------+------+------+----------+--------------------------+ | id | select_type | table | partitions | type | possible_keys | key | key_len | ref | rows | filtered | Extra | +----+-------------+-------+------------+-------+---------------+-------------+---------+------+------+----------+--------------------------+ | 1 | SIMPLE | tb3 | NULL | index | ix_pa_ch_mo | ix_pa_ch_mo | 2304 | NULL | 1 | 100.00 | Using where; Using index | +----+-------------+-------+------------+-------+---------------+-------------+---------+------+------+----------+--------------------------+ 1 row in set, 1 warning (0.00 sec) 结论: 查找组合索引后面两个列时，走索引 <type ---->indx>
