如何查看MySQL数据库状态及信息（内存、数据库、编码格式、表、列、索引等）

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1、简介

2、正文

2.1 查看所有数据库

2.2 查看正在使用的数据库

2.3 查看当前数据库中的表

2.5 显示授权用户及其权限

2.6 查看服务器错误或警告信息

2.7 查看建库语句和建表语句

2.8 查看数据库端口

2.9 查看数据库索引大小

2.10 查看数据库大小

2.11 查看最大连接数

2.12 查看当前线程相关信息

2.13 查看文件存储路径

2.14 查看数据库编码

2.15 帮助指令

1、简介

现如今我们操作数据库，都是使用现成的数据库管理工具，比如Navicat、SQLyog等等。这些工具能够提供可视化操作界面，大大的提升了我们的操作效率，但是这样往往让我们忘却了很多数据库语句，比如建表语句、查询数据库信息等。这篇文章我们学习几个非常有用的语句，便于在没有可视化工具的时候给到你帮助。

2、正文

2.1 查看所有数据库

mysql> SHOW DATABASES;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| liziba             |
| mysql              |
| performance_schema |
| sys                |
+--------------------+
5 rows in set (0.00 sec)

2.2 查看正在使用的数据库

此时未选择数据库，显示null

mysql> SELECT DATABASE();
+------------+
| DATABASE() |
+------------+
| NULL       |
+------------+
1 row in set (0.00 sec)

选择数据库liziba

mysql> USE liziba;
Database changed
mysql> SELECT DATABASE();
+------------+
| DATABASE() |
+------------+
| liziba     |
+------------+
1 row in set (0.00 sec)

2.3 查看当前数据库中的表

mysql> SHOW TABLES;
+------------------+
| Tables_in_liziba |
+------------------+
| user             |
+------------------+
1 row in set (0.00 sec)

2.4 查看表的列信息

mysql> SHOW COLUMNS FROM user;
+-------+--------------+------+-----+---------+----------------+
| Field | Type         | Null | Key | Default | Extra          |
+-------+--------------+------+-----+---------+----------------+
| id    | bigint(20)   | NO   | PRI | NULL    | auto_increment |
| name  | varchar(255) | NO   |     | NULL    |                |
| age   | int(11)      | NO   |     | NULL    |                |
| sex   | smallint(6)  | NO   |     | NULL    |                |
+-------+--------------+------+-----+---------+----------------+
4 rows in set (0.00 sec)

2.5 显示授权用户及其权限

查看所有用户的授权信息：

mysql> SHOW GRANTS;

查看具体用户的授权信息：

SHOW GRANTS FOR 'root'@'localhost';

2.6 查看服务器错误或警告信息

查看错误信息，这里我将ERRORS打成ERROES，服务器会产生一条错误日志

mysql> SHOW ERROES;
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'ERROES' at line 1
mysql>
mysql>
mysql> SHOW ERRORS;
+-------+------+----------------------------------------------------------------------------------------------------------------------------------------------------------+
| Level | Code | Message                                                                                                                                                  |
+-------+------+----------------------------------------------------------------------------------------------------------------------------------------------------------+
| Error | 1064 | You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'ERROES' at line 1 |
+-------+------+----------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> SHOW WARNINGS;
+-------+------+------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Level | Code | Message                                                                                                                                                    |
+-------+------+------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Error | 1064 | You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'WARRINGS' at line 1 |
+-------+------+------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 s

2.7 查看建库语句和建表语句

查看liziba数据库的建库语句

mysql> SHOW CREATE DATABASE liziba;
+----------+-----------------------------------------------------------------+
| Database | Create Database                                                 |
+----------+-----------------------------------------------------------------+
| liziba   | CREATE DATABASE `liziba` /*!40100 DEFAULT CHARACTER SET utf8 */ |
+----------+-----------------------------------------------------------------+
1 row in set (0.00 sec)

查看user 表的建表语句，注意提前使用use xxx

mysql> SHOW CREATE TABLE user;
+-------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table                                                                                                                                                                                                                                                                     |
+-------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| user  | CREATE TABLE `user` (`id` bigint(20) NOT NULL AUTO_INCREMENT COMMENT '主键',`name` varchar(255) NOT NULL COMMENT '用户名',`age` int(11) NOT NULL COMMENT '年龄',`sex` smallint(6) NOT NULL COMMENT '性别',PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 |
+-------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.01 sec)

2.8 查看数据库端口

如果你忘记了端口，可以查看端口信息（前提是你能的登录上来，哈哈哈！）

mysql> SHOW VARIABLES LIKE 'port';
+---------------+-------+
| Variable_name | Value |
+---------------+-------+
| port          | 3306  |
+---------------+-------+
1 row in set, 1 warning (0.00 sec)

2.9 查看数据库索引大小

首先我们使用数据库information_schema，这个数据库中记录了表的相关信息

mysql> use information_schema;
Database changed

查看tables表列，可以看到记录的表相关信息属性，其中index_length列，记录了表的索引大小单位是B，table_schema列记录了当前表所属的数据库。

我们可以根据table_schema = 'liziba'，查看当前数据库下索引的大小

mysql> SELECT CONCAT(ROUND(SUM(INDEX_LENGTH)/(1024*1024), 4), 'mb') AS 'Database Index Size'-> FROM tables-> WHERE table_schema = 'liziba';
+---------------------+
| Database Index Size |
+---------------------+
| 0.0000mb            |
+---------------------+
1 row in set (0.00 sec)

2.10 查看数据库大小

除了计算索引大小，我们也可以统计数据库的大小，只需要将表数据内存和索引数据内存加起来即可。

mysql> SELECT CONCAT(((ROUND(SUM(data_length), 4) + ROUND(SUM(index_length), 4)) / (1024 * 1024)), ' mb') AS 'Database Size'-> FROM tables-> WHERE table_schema = 'liziba';
+---------------+
| Database Size |
+---------------+
| 0.01562500 mb |
+---------------+
1 row in set (0.00 sec)

image.png

2.11 查看最大连接数

151 是默认的最大连接数

mysql> SHOW VARIABLES LIKE '%max_connections%';
+------------------------+-------+
| Variable_name          | Value |
+------------------------+-------+
| max_connections        | 151   |
| mysqlx_max_connections | 100   |
+------------------------+-------+
2 rows in set, 1 warning (0.00 sec)

2.12 查看当前线程相关信息

注意这里使用STATUS，可以查看线程相关状态，VARIABLES查看的是配置参数。如下查询可以看到连接数、创建了多少线程、正在运行的线程等信息

mysql> SHOW STATUS LIKE 'Threads%';
+-------------------+-------+
| Variable_name     | Value |
+-------------------+-------+
| Threads_cached    | 1     |
| Threads_connected | 3     |
| Threads_created   | 4     |
| Threads_running   | 2     |
+-------------------+-------+
4 rows in set (0.00 sec)

2.13 查看文件存储路径

mysql> SHOW VARIABLES LIKE '%datadir%';
+---------------+------------------------------+
| Variable_name | Value                        |
+---------------+------------------------------+
| datadir       | E:\mysql-8.0.15-winx64\data\ |
+---------------+------------------------------+
1 row in set, 1 warning (0.00 sec)

2.14 查看数据库编码

查看数据库编码很有作用，我们有时候在同步数据的时候会因为编码不同导致数据出现异常，我们可以通过如下方式查看数据库的编码格式。

mysql> SHOW VARIABLES LIKE 'collation%';
+----------------------+--------------------+
| Variable_name        | Value              |
+----------------------+--------------------+
| collation_connection | gbk_chinese_ci     |
| collation_database   | utf8_general_ci    |
| collation_server     | utf8mb4_0900_ai_ci |
+----------------------+--------------------+
3 rows in set, 1 warning (0.00 sec)

2.15 帮助指令

可以使用HELP指令查看指令。
比如HELP SHOW;

mysql> HELP SHOW;
Name: 'SHOW'
Description:
SHOW has many forms that provide information about databases, tables,
columns, or status information about the server. This section describes
those following:SHOW {BINARY | MASTER} LOGS
SHOW BINLOG EVENTS [IN 'log_name'] [FROM pos] [LIMIT [offset,] row_count]
SHOW CHARACTER SET [like_or_where]
SHOW COLLATION [like_or_where]
SHOW [FULL] COLUMNS FROM tbl_name [FROM db_name] [like_or_where]
SHOW CREATE DATABASE db_name
SHOW CREATE EVENT event_name
SHOW CREATE FUNCTION func_name
SHOW CREATE PROCEDURE proc_name
SHOW CREATE TABLE tbl_name
SHOW CREATE TRIGGER trigger_name
SHOW CREATE VIEW view_name
SHOW DATABASES [like_or_where]
SHOW ENGINE engine_name {STATUS | MUTEX}
SHOW [STORAGE] ENGINES
SHOW ERRORS [LIMIT [offset,] row_count]
SHOW EVENTS
SHOW FUNCTION CODE func_name
SHOW FUNCTION STATUS [like_or_where]
SHOW GRANTS FOR user
SHOW INDEX FROM tbl_name [FROM db_name]
SHOW MASTER STATUS
SHOW OPEN TABLES [FROM db_name] [like_or_where]
SHOW PLUGINS
SHOW PROCEDURE CODE proc_name
SHOW PROCEDURE STATUS [like_or_where]
SHOW PRIVILEGES
SHOW [FULL] PROCESSLIST
SHOW PROFILE [types] [FOR QUERY n] [OFFSET n] [LIMIT n]
SHOW PROFILES
SHOW RELAYLOG EVENTS [IN 'log_name'] [FROM pos] [LIMIT [offset,] row_count]
SHOW SLAVE HOSTS
SHOW SLAVE STATUS [FOR CHANNEL channel]
SHOW [GLOBAL | SESSION] STATUS [like_or_where]
SHOW TABLE STATUS [FROM db_name] [like_or_where]
SHOW [FULL] TABLES [FROM db_name] [like_or_where]
SHOW TRIGGERS [FROM db_name] [like_or_where]
SHOW [GLOBAL | SESSION] VARIABLES [like_or_where]
SHOW WARNINGS [LIMIT [offset,] row_count]

HELP STATUS;

mysql> HELP STATUS;
Many help items for your request exist.
To make a more specific request, please type 'help <item>',
where <item> is one of the following
topics:FLUSHSHOWSHOW ENGINESHOW FUNCTION STATUSSHOW MASTER STATUSSHOW PROCEDURE STATUSSHOW SLAVE STATUSSHOW STATUSSHOW TABLE STATUS