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Mysql查询数据库连接状态以及连接信息详解

 更新时间：2023年04月14日 08:41:53   作者：Super_龙  
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Mysql查询数据库连接状态及连接信息

使用MySQL时，需要了解当前数据库的情况，例如当前的数据库大小、字符集、用户等等。下面总结了一些查看数据库相关信息的命令

查看显示所有数据库

mysql> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| INVOICE            |
| mysql              |
| performance_schema |
| test               |
+--------------------+
5 rows in set (0.00 sec)
 
mysql>

查看当前使用的数据库

mysql> select database();
+------------+
| database() |
+------------+
| INVOICE    |
+------------+
1 row in set (0.00 sec)
 
mysql>

查看数据库使用端口

mysql> show variables  like 'port';
+---------------+-------+
| Variable_name | Value |
+---------------+-------+
| port          | 3306  |
+---------------+-------+
1 row in set (0.00 sec)

查看当前数据库大小

例如，我要查看INVOICE数据库的大小，那么可以通过下面SQL查看

mysql> use  information_schema
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A
 
Database changed
mysql> select concat(round(sum(data_length)/(1024*1024),2) + round(sum(index_length)/(1024*1024),2),'MB') as 'DB Size'
    -> from tables 
    -> where table_schema='INVOICE';
+-----------+
| DB Size   |
+-----------+
| 7929.58MB |
+-----------+
1 row in set, 1 warning (0.00 sec)

查看数据所占的空间大小

mysql> use information_schema;
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A
 
Database changed
mysql> select concat(round(sum(data_length)/(1024*1024),2),'MB') as 'DB Size'
    -> from tables
    -> where table_schema='INVOICE';
+-----------+
| DB Size   |
+-----------+
| 6430.26MB |
+-----------+
1 row in set, 1 warning (0.00 sec)
 
mysql>

查看索引所占的空间大小

mysql> select concat(round(sum(index_length)/(1024*1024),2),'MB') as 'DB Size' 
    -> from tables 
    -> where table_schema='INVOICE';
+-----------+
| DB Size   |
+-----------+
| 1499.32MB |
+-----------+
1 row in set, 1 warning (0.13 sec)
 
mysql>

查看数据库编码

mysql> show variables like 'character%';
+--------------------------+----------------------------+
| Variable_name            | Value                      |
+--------------------------+----------------------------+
| character_set_client     | utf8                       |
| character_set_connection | utf8                       |
| character_set_database   | utf8                       |
| character_set_filesystem | binary                     |
| character_set_results    | utf8                       |
| character_set_server     | latin1                     |
| character_set_system     | utf8                       |
| character_sets_dir       | /usr/share/mysql/charsets/ |
+--------------------------+----------------------------+
8 rows in set (0.00 sec)
  • character_set_client 为客户端编码方式；
  • character_set_connection 为建立连接使用的编码；
  • character_set_database 为数据库的编码；
  • character_set_results 为结果集的编码；
  • character_set_server 为数据库服务器的编码；

只要保证以上采用的编码方式一样，就不会出现乱码问题。

mysql> show variables like 'collation%';
+----------------------+-------------------+
| Variable_name        | Value             |
+----------------------+-------------------+
| collation_connection | utf8_general_ci   |
| collation_database   | utf8_general_ci   |
| collation_server     | latin1_swedish_ci |
+----------------------+-------------------+
3 rows in set (0.00 sec)

status也可以查看数据库的编码

mysql> status;
--------------
mysql  Ver 14.14 Distrib 5.6.20, for Linux (x86_64) using  EditLine wrapper
 
Connection id:          1
Current database:       INVOICE
Current user:           root@localhost
SSL:                    Not in use
Current pager:          stdout
Using outfile:          ''
Using delimiter:        ;
Server version:         5.6.20-enterprise-commercial-advanced MySQL Enterprise Server - Advanced Edition (Commercial)
Protocol version:       10
Connection:             Localhost via UNIX socket
Server characterset:    latin1
Db     characterset:    latin1
Client characterset:    utf8
Conn.  characterset:    utf8
UNIX socket:            /var/lib/mysql/mysql.sock
Uptime:                 5 hours 18 min 51 sec
 
Threads: 1  Questions: 10884  Slow queries: 0  Opens: 650  Flush tables: 1  Open tables: 268  Queries per second avg: 0.568
--------------
mysql>

查看数据库的表信息

mysql> show tables;
+---------------------------------------+
| Tables_in_information_schema          |
+---------------------------------------+
| CHARACTER_SETS                        |
| COLLATIONS                            |
| COLLATION_CHARACTER_SET_APPLICABILITY |
| COLUMNS                               |
| COLUMN_PRIVILEGES                     |
| ENGINES                               |
| EVENTS                                |
| FILES                                 |
| GLOBAL_STATUS                         |
| GLOBAL_VARIABLES                      |
| KEY_COLUMN_USAGE                      |
| OPTIMIZER_TRACE                       |
| PARAMETERS                            |
| PARTITIONS                            |
| PLUGINS                               |
| PROCESSLIST                           |
| PROFILING                             |
| REFERENTIAL_CONSTRAINTS               |
| ROUTINES                              |
| SCHEMATA                              |
| SCHEMA_PRIVILEGES                     |
| SESSION_STATUS                        |
| SESSION_VARIABLES                     |
| STATISTICS                            |
| TABLES                                |
| TABLESPACES                           |
| TABLE_CONSTRAINTS                     |
| TABLE_PRIVILEGES                      |
| TRIGGERS                              |
| USER_PRIVILEGES                       |
| VIEWS                                 |
| INNODB_LOCKS                          |
| INNODB_TRX                            |
| INNODB_SYS_DATAFILES                  |
| INNODB_LOCK_WAITS                     |
| INNODB_SYS_TABLESTATS                 |
| INNODB_CMP                            |
| INNODB_METRICS                        |
| INNODB_CMP_RESET                      |
| INNODB_CMP_PER_INDEX                  |
| INNODB_CMPMEM_RESET                   |
| INNODB_FT_DELETED                     |
| INNODB_BUFFER_PAGE_LRU                |
| INNODB_SYS_FOREIGN                    |
| INNODB_SYS_COLUMNS                    |
| INNODB_SYS_INDEXES                    |
| INNODB_FT_DEFAULT_STOPWORD            |
| INNODB_SYS_FIELDS                     |
| INNODB_CMP_PER_INDEX_RESET            |
| INNODB_BUFFER_PAGE                    |
| INNODB_CMPMEM                         |
| INNODB_FT_INDEX_TABLE                 |
| INNODB_FT_BEING_DELETED               |
| INNODB_SYS_TABLESPACES                |
| INNODB_FT_INDEX_CACHE                 |
| INNODB_SYS_FOREIGN_COLS               |
| INNODB_SYS_TABLES                     |
| INNODB_BUFFER_POOL_STATS              |
| INNODB_FT_CONFIG                      |
+---------------------------------------+
59 rows in set (0.00 sec)

或者使用下面SQL语句查看某个数据库的表信息。

select * from information_schema.tables where table_schema=‘databasename';

查看某种具体表的信息

select * from information_schema.tables where table_name =‘table_name'

查看数据库的所有用户信息

mysql>  select distinct concat('user: ''',user,'''@''',host,''';') as query from mysql.user;
+-------------------------------------+
| query                               |
+-------------------------------------+
| user: 'root'@'127.0.0.1';           |
| user: 'root'@'::1';                 |
| user: 'root'@'gettesx20.test.com'; |
| user: 'root'@'localhost';           |
+-------------------------------------+
4 rows in set (0.00 sec)
 
mysql>

查看某个具体用户的权限

mysql> show grants for 'root'@'localhost';
+---------------------------------------------------------------------------------------------------------------------------------+
| Grants for root@localhost                                                                                                              |
+---------------------------------------------------------------------------------------------------------------------------------+
| GRANT ALL PRIVILEGES ON *.* TO 'root'@'localhost' IDENTIFIED BY PASSWORD '*C7B1594FD74578DA3A92A61720AC67C6DBE6FC23' WITH GRANT OPTION |
| GRANT PROXY ON ''@'' TO 'root'@'localhost' WITH GRANT OPTION                                                                           |
+---------------------------------------------------------------------------------------------------------------------------------+
2 rows in set (0.00 sec)

查看数据库的最大连接数

mysql>  show variables like '%max_connections%';
+-----------------+-------+
| Variable_name   | Value |
+-----------------+-------+
| max_connections | 151   |
+-----------------+-------+
1 row in set (0.00 sec)
 
mysql>

查看数据库当前连接数，并发数。

mysql> show status like 'Threads%';
+-------------------+-------+
| Variable_name     | Value |
+-------------------+-------+
| Threads_cached    | 0     |
| Threads_connected | 1     |
| Threads_created   | 1     |
| Threads_running   | 1     |
+-------------------+-------+
4 rows in set (0.00 sec)

Threads_cached : 代表当前此时此刻线程缓存中有多少空闲线程。

Threads_connected :代表当前已建立连接的数量，因为一个连接就需要一个线程，所以也可以看成当前被使用的线程数。

Threads_created :代表从最近一次服务启动，已创建线程的数量。

Threads_running :代表当前激活的（非睡眠状态）线程数。并不是代表正在使用的线程数，有时候连接已建立，但是连接处于sleep状态，这里相对应的线程也是sleep状态。

查看数据文件存放路径

mysql> show variables like '%datadir%';
+---------------+-------------------+
| Variable_name | Value             |
+---------------+-------------------+
| datadir       | /mysqldata/mysql/ |
+---------------+-------------------+
1 row in set (0.00 sec)
 
mysql>

总结

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