mysql索引优化

mysql> create database test;
Query OK, 1 row affected (0.57 sec)

mysql> use test;
Database changed
mysql> show tables;
Empty set (0.00 sec)
mysql> create table t1(
    -> id int unsigned not null auto_increment primary key,
    -> name varchar(30)
    -> );
Query OK, 0 rows affected (0.05 sec)
mysql> show tables;
+----------------+
| Tables_in_test |
+----------------+
| t1             |
+----------------+
1 row in set (0.02 sec)
mysql> desc t1;
+-------+------------------+------+-----+---------+----------------+
| Field | Type             | Null | Key | Default | Extra          |
+-------+------------------+------+-----+---------+----------------+
| id    | int(10) unsigned | NO   | PRI | NULL    | auto_increment |
| name  | varchar(30)      | YES  |     | NULL    |                |
+-------+------------------+------+-----+---------+----------------+
2 rows in set (0.36 sec)

mysql> insert into t1(name) values ("user1");
Query OK, 1 row affected (0.11 sec)

mysql> insert into t1(name) values ("user2");
Query OK, 1 row affected (0.00 sec)

mysql> create table t2 like t1;
Query OK, 0 rows affected (0.08 sec)

mysql> describe t2;
+-------+------------------+------+-----+---------+----------------+
| Field | Type             | Null | Key | Default | Extra          |
+-------+------------------+------+-----+---------+----------------+
| id    | int(10) unsigned | NO   | PRI | NULL    | auto_increment |
| name  | varchar(30)      | YES  |     | NULL    |                |
+-------+------------------+------+-----+---------+----------------+
2 rows in set (0.01 sec)

mysql> insert into t2 select * from t1;
Query OK, 2 rows affected (0.18 sec)

mysql> select * from t2;
+----+-------+
| id | name  |
+----+-------+
|  1 | user1 |
|  2 | user2 |
+----+-------+
2 rows in set (0.00 sec)
mysql> create index in_name on t1(name);
Query OK, 0 rows affected (1.05 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> show index 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 | id          | A         |           2 |     NULL | NULL   |      | BTREE      |         |               |
| t1    |          1 | in_name  |            1 | name        | A         |           2 |     NULL | NULL   | YES  | BTREE      |         |               |
+-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
2 rows in set (0.00 sec)

mysql> drop index in_name on t1;
Query OK, 0 rows affected (0.24 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> alter table t1 add index in_name(name);
Query OK, 0 rows affected (0.36 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> alter table t1 drop index in_name;
Query OK, 0 rows affected (0.10 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> show session status;

mysql> show global status like "com_insert%";
+-------------------+-------+
| Variable_name     | Value |
+-------------------+-------+
| Com_insert        | 2     |
| Com_insert_select | 2     |
+-------------------+-------+
2 rows in set (0.00 sec)

mysql> show global status like "com_select%";
+---------------+-------+
| Variable_name | Value |
+---------------+-------+
| Com_select    | 135   |
+---------------+-------+
1 row in set (0.01 sec)

mysql> show global status like "com_update%";
+------------------+-------+
| Variable_name    | Value |
+------------------+-------+
| Com_update       | 0     |
| Com_update_multi | 0     |
+------------------+-------+
2 rows in set (0.00 sec)

mysql> show global status like "com_delete%";
+------------------+-------+
| Variable_name    | Value |
+------------------+-------+
| Com_delete       | 0     |
| Com_delete_multi | 0     |
+------------------+-------+
2 rows in set (0.00 sec)

mysql> delete from t2 where id=1;
Query OK, 1 row affected (0.10 sec)

mysql> show global status like "com_delete%";
+------------------+-------+
| Variable_name    | Value |
+------------------+-------+
| Com_delete       | 1     |
| Com_delete_multi | 0     |
+------------------+-------+
2 rows in set (0.00 sec)

mysql> show status like "innodb_rows%";
+----------------------+-------+
| Variable_name        | Value |
+----------------------+-------+
| Innodb_rows_deleted  | 1     |
| Innodb_rows_inserted | 10    |
| Innodb_rows_read     | 5     |
| Innodb_rows_updated  | 0     |
+----------------------+-------+
4 rows in set (0.00 sec)

mysql> show status like "connections%"
    -> ;
+---------------+-------+
| Variable_name | Value |
+---------------+-------+
| Connections   | 78    |
+---------------+-------+
1 row in set (0.00 sec)

mysql> show status like "slow_queries";
+---------------+-------+
| Variable_name | Value |
+---------------+-------+
| Slow_queries  | 0     |
+---------------+-------+
1 row in set (0.00 sec)


mysql> show variables like "%slow%";
+---------------------+--------------------------------+
| Variable_name       | Value                          |
+---------------------+--------------------------------+
| log_slow_queries    | OFF                            |
| slow_launch_time    | 2                              |
| slow_query_log      | OFF                            |
| slow_query_log_file | /var/lib/mysql/ubuntu-slow.log |
+---------------------+--------------------------------+
4 rows in set (0.00 sec)

mysql> show variables like "%long%";
+---------------------------------------------------+-----------+
| Variable_name                                     | Value     |
+---------------------------------------------------+-----------+
| long_query_time                                   | 10.000000 |
| max_long_data_size                                | 16777216  |
| performance_schema_events_waits_history_long_size | 10000     |
+---------------------------------------------------+-----------+
3 rows in set (0.00 sec)

mysql> desc select * from t1 \G;
*************************** 1. row ***************************
           id: 1
  select_type: SIMPLE
        table: t1
         type: ALL
possible_keys: NULL
          key: NULL
      key_len: NULL
          ref: NULL
         rows: 2
        Extra:
1 row in set (0.00 sec)

ERROR:
No query specified

mysql> explain select * from t1 \G;
*************************** 1. row ***************************
           id: 1
  select_type: SIMPLE
        table: t1
         type: ALL
possible_keys: NULL
          key: NULL
      key_len: NULL
          ref: NULL
         rows: 2
        Extra:
1 row in set (0.00 sec)

mysql> desc select * from t1 where name="user1" \G;
*************************** 1. row ***************************
           id: 1
  select_type: SIMPLE
        table: t1
         type: ALL
possible_keys: NULL
          key: NULL
      key_len: NULL
          ref: NULL
         rows: 6
        Extra: Using where
1 row in set (0.00 sec)

mysql> desc select * from t1 where id="1" \G;
*************************** 1. row ***************************
           id: 1
  select_type: SIMPLE
        table: t1
         type: const
possible_keys: PRIMARY
          key: PRIMARY
      key_len: 4
          ref: const
         rows: 1
        Extra:
1 row in set (0.30 sec)

mysql> show index from t1 \G;
*************************** 1. row ***************************
        Table: t1
   Non_unique: 0
     Key_name: PRIMARY
 Seq_in_index: 1
  Column_name: id
    Collation: A
  Cardinality: 6
     Sub_part: NULL
       Packed: NULL
         Null:
   Index_type: BTREE
      Comment:
Index_comment:
1 row in set (0.00 sec)

mysql> alter table t1 add index nameindex(name);
Query OK, 0 rows affected (0.21 sec)

mysql> desc select * from t1 where name="user1" \G;
*************************** 1. row ***************************
           id: 1
  select_type: SIMPLE
        table: t1
         type: ref
possible_keys: nameindex
          key: nameindex
      key_len: 33
          ref: const
         rows: 1
        Extra: Using where; Using index
1 row in set (0.00 sec)

mysql> explain select * from t1 where name like "%ser1" \G;
*************************** 1. row ***************************
           id: 1
  select_type: SIMPLE
        table: t1
         type: index
possible_keys: NULL
          key: nameindex
      key_len: 33
          ref: NULL
         rows: 6
        Extra: Using where; Using index
1 row in set (0.00 sec)

mysql> explain select * from t1 where name is not null \G;
*************************** 1. row ***************************
           id: 1
  select_type: SIMPLE
        table: t1
         type: index
possible_keys: nameindex
          key: nameindex
      key_len: 33
          ref: NULL
         rows: 6
        Extra: Using where; Using index
1 row in set (0.00 sec)

mysql> explain select * from t1 where name="user1" or id=2 \G;
*************************** 1. row ***************************
           id: 1
  select_type: SIMPLE
        table: t1
         type: index
possible_keys: PRIMARY,nameindex
          key: nameindex
      key_len: 33
          ref: NULL
         rows: 6
        Extra: Using where; Using index
1 row in set (0.00 sec)

mysql> alter table t1 drop index nameindex;

mysql> explain select * from t1 where name="user1" or id=2 \G;
*************************** 1. row ***************************
           id: 1
  select_type: SIMPLE
        table: t1
         type: ALL
possible_keys: PRIMARY
          key: NULL
      key_len: NULL
          ref: NULL
         rows: 6
        Extra: Using where
1 row in set (0.00 sec)
and or条件必须全建立了索引才能用到索引，另外必须使用数据库中的类型进行匹配。例如字符型的就不能用整数型的作为查询条件。

mysql> show status like "handler_read%";
+-----------------------+-------+
| Variable_name         | Value |
+-----------------------+-------+
| Handler_read_first    | 2     |
| Handler_read_key      | 11    |
| Handler_read_last     | 0     |
| Handler_read_next     | 0     |
| Handler_read_prev     | 0     |
| Handler_read_rnd      | 0     |
| Handler_read_rnd_next | 1160  |
+-----------------------+-------+
7 rows in set (0.00 sec)