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，那麼可以通過下面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 -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 -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 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，並發數。
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閒線程。
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。並不是代表正在使用的線程數，有時候連接已建立，但是連接處於sleep狀態，這裡相對應的線程也是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>
