使用MySQL時，需要了解當前數據庫的情況，例如當前的數據庫大小、字符集、用戶等等。下面總結了一些查看數據庫相關信息的命令

1：查看顯示所有數據庫

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

2：查看當前使用的數據庫

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

3：查看數據庫使用端口

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

4：查看當前數據庫大小

例如，我要查看INVOICE數據庫的大小，那么可以通過下面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 -ADatabase 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)

查看數據所占的空間大小

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 -ADatabase 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>

查看索引所占的空間大小

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：查看數據庫編碼

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????? 為客戶端編碼方式；

character_set_connection? 為建立連接使用的編碼；

character_set_database??? 為數據庫的編碼；

character_set_results???? 為結果集的編碼；

character_set_server????? 為數據庫服務器的編碼；

只要保證以上采用的編碼方式一樣，就不會出現亂碼問題。

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也可以查看數據庫的編碼

mysql> status; -------------- mysql Ver 14.14 Distrib 5.6.20, for Linux (x86_64) using EditLine wrapperConnection 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 secThreads: 1 Questions: 10884 Slow queries: 0 Opens: 650 Flush tables: 1 Open tables: 268 Queries per second avg: 0.568 -------------- mysql>

6：查看數據庫的表信息

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語句查看某個數據庫的表信息。

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

查看某種具體表的信息

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

7：查看數據庫的所有用戶信息

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: 查看某個具體用戶的權限

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： 查看數據庫的最大連接數

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

10：查看數據庫當前連接數，并發數。

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 : 代表當前此時此刻線程緩存中有多少空閑線程。

Threads_connected :代表當前已建立連接的數量，因為一個連接就需要一個線程，所以也可以看成當前被使用的線程數。

Threads_created :代表從最近一次服務啟動，已創建線程的數量。

Threads_running :代表當前激活的（非睡眠狀態）線程數。并不是代表正在使用的線程數，有時候連接已建立，但是連接處于sleep狀態，這里相對應的線程也是sleep狀態。

11：查看數據文件存放路徑

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

總結

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