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>
2：查看当前使用的数据库
mysql> select database(); +------------+ | database() | +------------+ | INVOICE | +------------+ 1 row in set (0.00 sec) mysql>
![clip_image001[1]](http://images0.cnblogs.com/blog/73542/201506/282355422209021.png "clip_image001[1]")
3：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)
![clip_image002[1]](http://images0.cnblogs.com/blog/73542/201506/282355431743566.png "clip_image002[1]")
4：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>
5：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)
![clip_image003[1]](http://images0.cnblogs.com/blog/73542/201506/282355442525136.png "clip_image003[1]")
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>
6：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'
7：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>
8: 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)
9： 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>
10：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。
11：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>