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

  1. 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>
  1. 查看当前使用的数据库
mysql> select database();+------------+| database() |+------------+| INVOICE|+------------+1 row in set (0.00 sec) mysql>
  1. 查看数据库使用端口
mysql> show variableslike 'port';+---------------+-------+| Variable_name | Value |+---------------+-------+| port| 3306|+---------------+-------+1 row in set (0.00 sec)
  1. 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> useinformation_schemaReading table information for completion of table and column namesYou can turn off this feature to get a quicker startup with -A Database changedmysql> 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)
  1. 查看数据所占的空间大小
mysql> use information_schema;Reading table information for completion of table and column namesYou can turn off this feature to get a quicker startup with -A Database changedmysql> 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>
  1. 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>
  1. 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;--------------mysqlVer 14.14 Distrib 5.6.20, for Linux (x86_64) usingEditLine wrapper Connection id:1Current database: INVOICECurrent user: root@localhostSSL:Not in useCurrent pager:stdoutUsing outfile:''Using delimiter:;Server version: 5.6.20-enterprise-commercial-advanced MySQL Enterprise Server - Advanced Edition (Commercial)Protocol version: 10Connection: Localhost via UNIX socketServer characterset:latin1Db characterset:latin1Client characterset:utf8Conn.characterset:utf8UNIX socket:/var/lib/mysql/mysql.sockUptime: 5 hours 18 min 51 sec Threads: 1Questions: 10884Slow queries: 0Opens: 650Flush tables: 1Open tables: 268Queries per second avg: 0.568--------------mysql>
  1. 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’

  1. ：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>
  1. 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)
  1. 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>
  1. 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。

  1. 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>