MySQL常用命令、配置汇总

MySQL 5.7.21 on Ubuntu

---

按照8020法则，整理常用的MySQL命令、配置。

目录

常用命令

1、help
2、show命令
3、EXPLAIN | DESCRIBE | DESC
4、数据库
5、用户
6、权限
7、数据表及字段
8、索引

常用配置

1、服务器配置

参考文档

常用命令

1、help

help 或 ?

help contents

help <item>

2、show命令

help show

SHOW CHARACTER SET [like_or_where]

SHOW COLLATION [like_or_where]

SHOW CREATE DATABASE db_name

SHOW CREATE TABLE tbl_name

SHOW DATABASES [like_or_where]

SHOW [FULL] PROCESSLIST

SHOW [GLOBAL | SESSION] VARIABLES [like_or_where]

mysql> show table status G;

查看存储引擎：来自博客园

mysql> show Storage Engines; -- 来自 help contents
+--------------------+---------+----------------------------------------------------------------+--------------+------+------------+
| Engine             | Support | Comment                                                        | Transactions | XA   | Savepoints |
+--------------------+---------+----------------------------------------------------------------+--------------+------+------------+
| InnoDB             | DEFAULT | Supports transactions, row-level locking, and foreign keys     | YES          | YES  | YES        |
| MRG_MYISAM         | YES     | Collection of identical MyISAM tables                          | NO           | NO   | NO         |
| MEMORY             | YES     | Hash based, stored in memory, useful for temporary tables      | NO           | NO   | NO         |
| BLACKHOLE          | YES     | /dev/null storage engine (anything you write to it disappears) | NO           | NO   | NO         |
| MyISAM             | YES     | MyISAM storage engine                                          | NO           | NO   | NO         |
| CSV                | YES     | CSV storage engine                                             | NO           | NO   | NO         |
| ARCHIVE            | YES     | Archive storage engine                                         | NO           | NO   | NO         |
| PERFORMANCE_SCHEMA | YES     | Performance Schema                                             | NO           | NO   | NO         |
| FEDERATED          | NO      | Federated MySQL storage engine                                 | NULL         | NULL | NULL       |
+--------------------+---------+----------------------------------------------------------------+--------------+------+------------+
9 rows in set (0.00 sec)

3、EXPLAIN | DESCRIBE | DESC

三者是同一个命令。

The DESCRIBE and EXPLAIN statements are synonyms（同义词）. In practice, the
DESCRIBE keyword is more often used to obtain information about table
structure, whereas EXPLAIN is used to obtain a query execution plan
(that is, an explanation of how MySQL would execute a query).

用途：来自博客园

1）查看数据表结构（及字段），常用DESC

DESC使用

mysql> show tables;
+-----------------+
| Tables_in_gitee |
+-----------------+
| user            |
+-----------------+
1 row in set (0.00 sec)

mysql> desc user;
+--------------------+--------------+------+-----+-------------------+-----------------------------+
| Field              | Type         | Null | Key | Default           | Extra                       |
+--------------------+--------------+------+-----+-------------------+-----------------------------+
| id                 | bigint(20)   | NO   | PRI | NULL              | auto_increment              |
| age                | int(11)      | YES  |     | 0                 |                             |
| create_time        | datetime     | YES  |     | CURRENT_TIMESTAMP |                             |
| email              | varchar(255) | NO   | UNI |                   |                             |
| name               | varchar(100) | NO   |     | NULL              |                             |
| nick_name          | varchar(200) | NO   | UNI | NULL              |                             |
| password           | varchar(384) | NO   |     | NULL              |                             |
| password_algorithm | varchar(20)  | NO   |     | NULL              |                             |
| password_salt      | varchar(20)  | NO   |     | NULL              |                             |
| phone              | varchar(20)  | NO   | UNI |                   |                             |
| sex                | int(11)      | YES  |     | NULL              |                             |
| update_time        | datetime     | YES  |     | CURRENT_TIMESTAMP | on update CURRENT_TIMESTAMP |
+--------------------+--------------+------+-----+-------------------+-----------------------------+
12 rows in set (0.01 sec)

mysql> desc user age;
+-------+---------+------+-----+---------+-------+
| Field | Type    | Null | Key | Default | Extra |
+-------+---------+------+-----+---------+-------+
| age   | int(11) | YES  |     | 0       |       |
+-------+---------+------+-----+---------+-------+
1 row in set (0.01 sec)

2）分析SQL命令，常用EXPLAIN

EXPLAIN分析

mysql> explain insert into user(age,first_name,last_name,name) value(12,'lib','Ma','user090801');
+----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+-------+
| id | select_type | table | partitions | type | possible_keys | key  | key_len | ref  | rows | filtered | Extra |
+----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+-------+
|  1 | INSERT      | user  | NULL       | ALL  | NULL          | NULL | NULL    | NULL | NULL |     NULL | NULL  |
+----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+-------+
1 row in set (0.00 sec)
# 在EXPLAIN后执行INSERT，只是分析，没有添加用户
mysql> select * from user;
+----+------+---------------------+------------+-----------+---------------------+------+------+
| id | age  | create_time         | first_name | last_name | update_time         | name | sex  |
+----+------+---------------------+------------+-----------+---------------------+------+------+
|  2 |    0 | 2021-08-21 16:03:14 | Chloe      | O'Brian   | 2021-08-21 16:03:14 |      | NULL |
|  3 |    0 | 2021-08-21 16:03:14 | Kim        | Bauer     | 2021-08-21 16:03:14 |      | NULL |
|  4 |    0 | 2021-08-21 16:03:14 | David      | Palmer    | 2021-08-21 16:03:14 |      | NULL |
|  5 |    0 | 2021-08-21 16:03:14 | Michelle   | Dessler   | 2021-08-21 16:03:14 |      | NULL |
|  6 |   27 | 2021-08-22 09:25:48 | He         | Li        | 2021-08-22 09:37:44 |      | NULL |
+----+------+---------------------+------------+-----------+---------------------+------+------+
5 rows in set (0.00 sec)

mysql>
mysql> insert into user(age,first_name,last_name,name) value(12,'lib','Ma','user090801');
Query OK, 1 row affected (0.01 sec)

mysql> select * from user;
+----+------+---------------------+------------+-----------+---------------------+------------+------+
| id | age  | create_time         | first_name | last_name | update_time         | name       | sex  |
+----+------+---------------------+------------+-----------+---------------------+------------+------+
|  2 |    0 | 2021-08-21 16:03:14 | Chloe      | O'Brian   | 2021-08-21 16:03:14 |            | NULL |
|  3 |    0 | 2021-08-21 16:03:14 | Kim        | Bauer     | 2021-08-21 16:03:14 |            | NULL |
|  4 |    0 | 2021-08-21 16:03:14 | David      | Palmer    | 2021-08-21 16:03:14 |            | NULL |
|  5 |    0 | 2021-08-21 16:03:14 | Michelle   | Dessler   | 2021-08-21 16:03:14 |            | NULL |
|  6 |   27 | 2021-08-22 09:25:48 | He         | Li        | 2021-08-22 09:37:44 |            | NULL |
|  7 |   12 | 2021-09-08 22:05:04 | lib        | Ma        | 2021-09-08 22:05:04 | user090801 | NULL |
+----+------+---------------------+------------+-----------+---------------------+------------+------+
6 rows in set (0.00 sec)

# 查看表user的所有
mysql> show index from user;
+-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |
+-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| user  |          0 | PRIMARY  |            1 | id          | A         |           6 |     NULL | NULL   |      | BTREE      |         |               |
| user  |          1 | idx_fn   |            1 | first_name  | A         |           6 |     NULL | NULL   |      | BTREE      |         |               |
+-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
2 rows in set (0.00 sec)

# 使用explain来分析各种select语句
mysql> explain select * from user where first_name = 'lib';
+----+-------------+-------+------------+------+---------------+--------+---------+-------+------+----------+-------+
| id | select_type | table | partitions | type | possible_keys | key    | key_len | ref   | rows | filtered | Extra |
+----+-------------+-------+------------+------+---------------+--------+---------+-------+------+----------+-------+
|  1 | SIMPLE      | user  | NULL       | ref  | idx_fn        | idx_fn | 102     | const |    1 |   100.00 | NULL  |
+----+-------------+-------+------------+------+---------------+--------+---------+-------+------+----------+-------+
1 row in set, 1 warning (0.00 sec)

mysql> explain select * from user where first_name = 'lib' and last_name = 'Ma';
+----+-------------+-------+------------+------+---------------+--------+---------+-------+------+----------+-------------+
| id | select_type | table | partitions | type | possible_keys | key    | key_len | ref   | rows | filtered | Extra       |
+----+-------------+-------+------------+------+---------------+--------+---------+-------+------+----------+-------------+
|  1 | SIMPLE      | user  | NULL       | ref  | idx_fn        | idx_fn | 102     | const |    1 |    16.67 | Using where |
+----+-------------+-------+------------+------+---------------+--------+---------+-------+------+----------+-------------+
1 row in set, 1 warning (0.00 sec)

mysql> explain select * from user where first_name = 'lib' and last_name = 'zhao';
+----+-------------+-------+------------+------+---------------+--------+---------+-------+------+----------+-------------+
| id | select_type | table | partitions | type | possible_keys | key    | key_len | ref   | rows | filtered | Extra       |
+----+-------------+-------+------------+------+---------------+--------+---------+-------+------+----------+-------------+
|  1 | SIMPLE      | user  | NULL       | ref  | idx_fn        | idx_fn | 102     | const |    1 |    16.67 | Using where |
+----+-------------+-------+------------+------+---------------+--------+---------+-------+------+----------+-------------+
1 row in set, 1 warning (0.00 sec)

mysql> explain select * from user where last_name = 'zhao';
+----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+-------------+
| id | select_type | table | partitions | type | possible_keys | key  | key_len | ref  | rows | filtered | Extra       |
+----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+-------------+
|  1 | SIMPLE      | user  | NULL       | ALL  | NULL          | NULL | NULL    | NULL |    6 |    16.67 | Using where |
+----+-------------+-------+------------+------+---------------+------+---------+------+------+----------+-------------+
1 row in set, 1 warning (0.01 sec)

explain更多信息，可以看 参考文档4 以及其他网友的好文。

4、数据库

创建：来自博客园

早期的UTF-8编码，不支持emoji表情等：

CREATE DATABASE IF NOT EXISTS dbname DEFAULT CHARSET utf8 COLLATE utf8_general_ci;

真正的UTF-8编码：

CREATE DATABASE IF NOT EXISTS dbname DEFAULT CHARSET utf8mb4 COLLATE utf8mb4_general_ci;

切换（选择）数据库：

USE db_name

显示当前数据库信息：

status

删除数据库：

DROP DATABASE IF EXISTS db_name;

修改数据库字符集：

ALTER DATABASE CHARACTER SET utf8 COLLATE utf8_general_ci;

5、用户

系统用户表：mysql.user

添加：来自博客园

默认Host为 %：'test4'@'%'

CREATE USER test1 IDENTIFIED BY '123';

设置（修改）密码：

1）ALTER USER test1 IDENTIFIED BY '111';

2）SET PASSWORD FOR test1 = '222';

3）SET PASSWORD FOR test1 = PASSWORD('222');

删除：

DROP USER IF EXISTS TEST3,test4;

6、权限

GRAMT 授权

REVOKE 回收权限

用户对：全局、数据库、表、列、存储过程、代理的权限

查看权限：来自博客园

SHOW GRANTS FOR user@host;

授予所有权限：

第一个* 表示 数据库，第二个*表示数据表（也可能是其它？）

GRANT ALL PRIVILEGES ON *.* TO user@host; 

授予查询权限：

GRANT SELECT ON db_example.* TO user@host;

回收所有权限：

REVOKE ALL PRIVILEGES ON *.* FROM user@host;

回收查询权限：

REVOKE SELECT ON db_example.* FROM 'test2'@'localhost';

刷新权限：

REVODE、DROP USER后执行

FLUSH PRIVILEGES;

7、数据表及字段

5种约束：

1. 默认 DEFAULT
2. 非空 NOT NULL 
3.  唯一 UNIQUE 也是 唯一性索引
4. 主键 PRIMARY KEY 也是 主键索引
5. 外键 [CONSTRAINT fk_name] FOREIGN KEY...REFERENCES

自动增长：AUTO_INCREMENT

一个表一个；

定义为间：UNIQUE KEY，PRIMARY KEY；

从1开始；

以上 约束、自动增长 的关键词添加到 字段类型 后面即可生效。来自博客园

数据类型：

数字类型

TINYINT SMALLINT MEDIUMINT INT BIGINT

FLOAT DOUBLE

DECIMAL(M,D)

BIT(M)

时间和日期类型

YEAR DATE TIME

DATETIME 1000~9999年，NOW()函数

TIMESTAMP 时间戳，1970~2038年，CURRENT_TIMESTAMP，默认情况下，自动设置 NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP

字符串类型

CHAR VARCHAR

TINYTEXT TEXT MEDIUMTEXT LONGTEXT

ENUM

SET

BINARY VARBINARY

BLOB

JSON 5.7.8开始支持

创建数据表：

2个字段：id、name

CREATE TABLE table1(id INT, name VARCHAR(32));

查看数据表的创建语句：来自博客园

里面会包含数据表的 引擎、默认字符集。

SHOW CREATE TABLE table1;

修改数据表字符集：

会影响新增字段的默认字符集。

ALTER TABLE table1 CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci;

查看数据表status：

当前数据库下所有表，末尾的 G 表示 结果竖着展示。

show table status G

查看数据表结构：

show full columns from table1;

可以看到字符集、评论等更多信息。

注，没有full时，和desc table1;相同。

mysql> show full columns from table1;
+-------+-------------+-----------------+------+-----+---------+-------+---------------------------------+---------+
| Field | Type        | Collation       | Null | Key | Default | Extra | Privileges                      | Comment |
+-------+-------------+-----------------+------+-----+---------+-------+---------------------------------+---------+
| id    | int(11)     | NULL            | YES  |     | NULL    |       | select,insert,update,references |         |
| name  | varchar(32) | utf8_general_ci | YES  |     | NULL    |       | select,insert,update,references |         |
+-------+-------------+-----------------+------+-----+---------+-------+---------------------------------+---------+
2 rows in set (0.00 sec)

查看所有数据表：

show tables; -- 当前数据库下的所有表

show tables from db_name; -- 数据库db_name下的所有表

删除数据表：来自博客园

DROP TABLE IF EXISTS table1;

查看字段信息：

desc table1 name;

修改字段名：

新字段类型是必须的。

ALTER TABLE table1 CHANGE name newname VARCHAR(32);

修改字段类型：

ALTER TABLE table1 MODIFY newname DATETIME;

新增字段：

ALTER TABLE table1 ADD age INT;

ALTER TABLE table1 ADD address VARCHAR(500); -- 字符集沿用数据表的

删除字段：

ALTER TABLE table1 DROP love;

8、索引

常见的5种索引：来自博客园

1. 普通索引 INDEX 或 KEY
2. 唯一性索引 
3. 主键索引 （聚簇cu4索引）
4. 全文索引 FULLTEXT INDEX，CHAR、VARCHAR、TEXT类型适用
5. 空间索引 SPATIAL INDEX

分类法2：单列索引、复合索引

查询数据表的索引：

show index from table1;

查询表的索引

mysql> show index from user;
+-------+------------+-----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| Table | Non_unique | Key_name  | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |
+-------+------------+-----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| user  |          0 | PRIMARY   |            1 | id          | A         |           1 |     NULL | NULL   |      | BTREE      |         |               |
| user  |          0 | email     |            1 | email       | A         |           1 |     NULL | NULL   |      | BTREE      |         |               |
| user  |          0 | nick_name |            1 | nick_name   | A         |           1 |     NULL | NULL   |      | BTREE      |         |               |
| user  |          0 | phone     |            1 | phone       | A         |           1 |     NULL | NULL   |      | BTREE      |         |               |
+-------+------------+-----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
4 rows in set (0.00 sec)

mysql>
mysql> desc user;
+--------------------+--------------+------+-----+-------------------+-----------------------------+
| Field              | Type         | Null | Key | Default           | Extra                       |
+--------------------+--------------+------+-----+-------------------+-----------------------------+
| id                 | bigint(20)   | NO   | PRI | NULL              | auto_increment              |
| age                | int(11)      | YES  |     | 0                 |                             |
| create_time        | datetime     | YES  |     | CURRENT_TIMESTAMP |                             |
| email              | varchar(255) | NO   | UNI |                   |                             |
| name               | varchar(100) | NO   |     | NULL              |                             |
| nick_name          | varchar(200) | NO   | UNI | NULL              |                             |
| password           | varchar(384) | NO   |     | NULL              |                             |
| password_algorithm | varchar(20)  | NO   |     | NULL              |                             |
| password_salt      | varchar(20)  | NO   |     | NULL              |                             |
| phone              | varchar(20)  | NO   | UNI |                   |                             |
| sex                | int(11)      | YES  |     | NULL              |                             |
| update_time        | datetime     | YES  |     | CURRENT_TIMESTAMP | on update CURRENT_TIMESTAMP |
+--------------------+--------------+------+-----+-------------------+-----------------------------+
12 rows in set (0.01 sec)

添加索引：来自博客园

CREATE TABLE时：

添加索引1

mysql> CREATE TABLE table2(id bigint PRIMARY KEY, name varchar(50) UNIQUE, age int DEFAULT 0, introduction varchar(200) DEFAULT '',
    -> INDEX idx_age (age DESC),
    -> FULLTEXT idx_ft_intro (introduction ASC));
Query OK, 0 rows affected (0.30 sec)

mysql> show index from table2;
+--------+------------+--------------+--------------+--------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| Table  | Non_unique | Key_name     | Seq_in_index | Column_name  | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |
+--------+------------+--------------+--------------+--------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| table2 |          0 | PRIMARY      |            1 | id           | A         |           0 |     NULL | NULL   |      | BTREE      |         |               |
| table2 |          0 | name         |            1 | name         | A         |           0 |     NULL | NULL   | YES  | BTREE      |         |               |
| table2 |          1 | idx_age      |            1 | age          | A         |           0 |     NULL | NULL   | YES  | BTREE      |         |               |
| table2 |          1 | idx_ft_intro |            1 | introduction | NULL      |           0 |     NULL | NULL   | YES  | FULLTEXT   |         |               |
+--------+------------+--------------+--------------+--------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
4 rows in set (0.00 sec)

ALTER TABLE时：

添加索引2

mysql> CREATE TABLE table3(id bigint, name varchar(50), age int DEFAULT 0, introduction varchar(200) DEFAULT '');
Query OK, 0 rows affected (0.02 sec)

# 没有任何索引
mysql> show index from table3;
Empty set (0.00 sec)

# 添加主键索引
mysql>
mysql> ALTER TABLE table3
    -> ADD PRIMARY KEY (id);
Query OK, 0 rows affected (0.06 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql>
mysql> show index from table3;
+--------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| Table  | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |
+--------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| table3 |          0 | PRIMARY  |            1 | id          | A         |           0 |     NULL | NULL   |      | BTREE      |         |               |
+--------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
1 row in set (0.00 sec)

mysql>
# 添加唯一索引
mysql> ALTER TABLE table3
    -> ADD UNIQUE (name);
Query OK, 0 rows affected (0.02 sec)
Records: 0  Duplicates: 0  Warnings: 0

# 添加普通索引
mysql> ALTER TABLE table3
    -> ADD INDEX idx_age (age DESC);
Query OK, 0 rows affected (0.02 sec)
Records: 0  Duplicates: 0  Warnings: 0

# 添加全文索引
mysql> ALTER TABLE table3
    -> ADD FULLTEXT ft1 (introduction);
Query OK, 0 rows affected, 1 warning (0.65 sec)
Records: 0  Duplicates: 0  Warnings: 1

mysql>
# 检查ALTER 添加的索引
mysql> show index from table3;
+--------+------------+----------+--------------+--------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| Table  | Non_unique | Key_name | Seq_in_index | Column_name  | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |
+--------+------------+----------+--------------+--------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| table3 |          0 | PRIMARY  |            1 | id           | A         |           0 |     NULL | NULL   |      | BTREE      |         |               |
| table3 |          0 | name     |            1 | name         | A         |           0 |     NULL | NULL   | YES  | BTREE      |         |               |
| table3 |          1 | idx_age  |            1 | age          | A         |           0 |     NULL | NULL   | YES  | BTREE      |         |               |
| table3 |          1 | ft1      |            1 | introduction | NULL      |           0 |     NULL | NULL   | YES  | FULLTEXT   |         |               |
+--------+------------+----------+--------------+--------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
4 rows in set (0.00 sec)

mysql>

CREATE [UNIQUE|FULLTEXT|SPATIAL] INDEX时：来自博客园

不能添加主键索引

添加复合索引：

添加索引3-复合

mysql> ALTER TABLE table3
    -> ADD INDEX comp_idx_1 (name ASC, age DESC);
Query OK, 0 rows affected (0.02 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> show index from table3;
+--------+------------+------------+--------------+--------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| Table  | Non_unique | Key_name   | Seq_in_index | Column_name  | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |
+--------+------------+------------+--------------+--------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| table3 |          0 | PRIMARY    |            1 | id           | A         |           0 |     NULL | NULL   |      | BTREE      |         |               |
| table3 |          0 | name       |            1 | name         | A         |           0 |     NULL | NULL   | YES  | BTREE      |         |               |
| table3 |          1 | idx_age    |            1 | age          | A         |           0 |     NULL | NULL   | YES  | BTREE      |         |               |
| table3 |          1 | comp_idx_1 |            1 | name         | A         |           0 |     NULL | NULL   | YES  | BTREE      |         |               |
| table3 |          1 | comp_idx_1 |            2 | age          | A         |           0 |     NULL | NULL   | YES  | BTREE      |         |               |
| table3 |          1 | ft1        |            1 | introduction | NULL      |           0 |     NULL | NULL   | YES  | FULLTEXT   |         |               |
+--------+------------+------------+--------------+--------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
6 rows in set (0.00 sec)

删除索引：

删除主键索引：

如果主键字段有AUTO_INCREMENT属性，需要先删除该属性。（少用）

ALTER TABLE 数据表 DROP PRIMARY KEY

删除非主键索引：来自博客园

ALTER TABLE 数据表 DROP INDEX 索引名

DROP INDEX 索引名 ON 数据表

删除索引

# 删除非主键索引
mysql> ALTER TABLE table3 DROP INDEX ft1;
Query OK, 0 rows affected (0.03 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> DROP INDEX comp_idx_1 ON table3;
Query OK, 0 rows affected (0.02 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql>
mysql> show index from table3;
+--------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| Table  | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |
+--------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| table3 |          0 | PRIMARY  |            1 | id          | A         |           0 |     NULL | NULL   |      | BTREE      |         |               |
| table3 |          0 | name     |            1 | name        | A         |           0 |     NULL | NULL   | YES  | BTREE      |         |               |
| table3 |          1 | idx_age  |            1 | age         | A         |           0 |     NULL | NULL   | YES  | BTREE      |         |               |
+--------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
3 rows in set (0.00 sec)


# 删除主键索引
# PRIMARY前后有 反引号（Tab键上面的按键），否则，失败
mysql> DROP INDEX PRIMARY ON table3;
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'PRIMARY ON table3' at line 1
mysql>
mysql> DROP INDEX `PRIMARY` ON table3;
Query OK, 0 rows affected (0.13 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> show index from table3;
+--------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| Table  | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |
+--------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| table3 |          0 | name     |            1 | name        | A         |           0 |     NULL | NULL   | YES  | BTREE      |         |               |
| table3 |          1 | idx_age  |            1 | age         | A         |           0 |     NULL | NULL   | YES  | BTREE      |         |               |
+--------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
2 rows in set (0.00 sec)

常用配置

1、服务器配置

配置分为：基本配置，优化配置，还有高级配置——比如，集群配置等。

本文的Ubuntu使用apt安装，默认建立了 mysql用户及用户组，并将mysql添加到了自启动服务中。

命令mysql：链接MySQL服务器，/usr/bin/mysql

命令mysqld：启动服务器，/usr/sbin/mysqld

服务器配置文件：/etc/mysql中，，其中的 mysqld.cnf 是服务器配置文件

区段：来自博客园

[client] 不常用

[mysqld] 常用

[mysqld]配置：mysqld.cnf 中 及 额外的配置

配置	说明
port	服务器端口，默认3306
datadir	数据目录，默认/var/lib/mysql
bind-address	服务器绑定的IP地址，默认注释掉
max_connections	客户端最大连接数，默认151（show variables like '%max_conn%';）
query_cache_limit	查询缓存限制，默认1M
query_cache_size	查询缓存大小，默认16M
log_error	错误日志，默认/var/log/mysql/error.log
slow_query_log	慢查询日志，默认1
slow_query_log_file	慢查询日志文件，/var/log/mysql/mysql-slow.log
long_query_time	查询超过指定时间时，日志会记录到慢查询日志中，默认2（单位是 秒？）
log-queries-not-using-indexes	是否在慢查询日志中记录 未使用索引查询
log-bin	二进制日志保存路径，主要用于 复制环境 和 数据恢复（重要）
max_binlog-size	二进制日志单个文件的大小限制，默认100M
expire_logs_days	自动删除超过指定天数的过期日志
key_buffer_size	索引缓冲区大小，由所有线程共享。增大可以更好处理索引。
innodb_log_file_size	Redo log的空间通过innodb_log_file_size和innodb_log_files_in_group参数来调节。
innodb_lock_wait_timeout	InnoDB的锁等待超时时间，默认50秒。

还有更多配置待解锁...来自博客园

参考文档

1、《MySQL数据库原理、设计与应用》

作者：黑马程序员，2019年4月第1版

2、MySQL中数据类型介绍

3、如何设置innodb_log_file_size

4、MySQL Explain详解

5、