[MySQL from entry to proficiency] Sharing of commonly used SQL statements

Foreword:

In daily work or study, we may often use certain SQLs. It is recommended that you organize and record these commonly used SQLs, which will be much more convenient for subsequent use. The author also compiled the SQL that I commonly use during work and study, and now I will share it with you! There may be some SQL that you don't use frequently, but I still hope it will be helpful to you. Maybe you can use it if you need it one day.

Note: The SQL shared below is applicable to MySQL 5.7 version, and lower versions may be slightly different. Some SQL may require higher permissions to execute.

1.show related statements

# 查看实例参数 例如：
show variables like '%innodb%';
show global variables like '%innodb%';

# 查看实例状态，例如：
show status like 'uptime%';
show global status like 'connection%';

# 查看数据库链接：
show processlist;
show full processlist;

# 查询某个表的结构：
show create table tb_name;

# 查询某个表的详细字段信息：
show full columns from tb_name;

# 查询某个表的全部索引信息：
show index from tb_name;

# 查询某个库以cd开头的表：
show tables like 'cd%';

# 查询某个库中的所有视图：
show table status where comment='view';

# 查询某个用户的权限：
show grants for 'test_user'@'%';

2. View account related information

# 这里先介绍下CONCAT函数：在MySQL中 CONCAT()函数用于将多个字符串连接成一个字符串，
利用此函数我们可以将原来一步无法得到的sql拼接出来，后面部分语句有用到该函数。
# 当拼接字符串中出现''时 需使用\转义符

# 查看所有用户名：
SELECT DISTINCT
	CONCAT(
		'User: \'',
		user,
		'\'@\'',
		host,
		'\';'
	) AS QUERY
FROM
	mysql.user;

# 查看用户详细信息：
SELECT user,
	host,
	authentication_string,
	password_expired,
	password_lifetime,
	password_last_changed,
	account_locked 
FROM
	mysql.user;

3.KILL database link

# 下面列举SQL只是拼接出kill 链接的语句，若想执行 直接将结果复制执行即可。
# 杀掉空闲时间大于2000s的链接：
SELECT
	concat( 'KILL ', id, ';' ) 
FROM
	information_schema.`PROCESSLIST` 
WHERE
	Command = 'Sleep' 
	AND TIME > 2000;
  
# 杀掉处于某状态的链接：
SELECT
	concat( 'KILL ', id, ';' ) 
FROM
	information_schema.`PROCESSLIST` 
WHERE
	STATE LIKE 'Creating sort index';
  
# 杀掉某个用户的链接：
SELECT
	concat( 'KILL ', id, ';' ) 
FROM
	information_schema.`PROCESSLIST` 
WHERE
	where user='root';

4. Splice to create database or user statements

# 拼接创建数据库语句（排除系统库）：
SELECT
	CONCAT(
		'create database ',
		'`',
    SCHEMA_NAME,
    '`',
    ' DEFAULT CHARACTER SET ',
    DEFAULT_CHARACTER_SET_NAME,
		';'
	) AS CreateDatabaseQuery
FROM
	information_schema.SCHEMATA
WHERE
	SCHEMA_NAME NOT IN (
		'information_schema',
		'performance_schema',
		'mysql',
		'sys'
	);
    
# 拼接创建用户语句（排除系统用户）：
SELECT
	CONCAT(
		'create user \'',
    user,
    '\'@\'',
    Host,
    '\''
    ' IDENTIFIED BY PASSWORD \'',
    authentication_string,
		'\';'
	) AS CreateUserQuery
FROM
	mysql.`user`
WHERE
	`User` NOT IN (
		'root',
		'mysql.session',
		'mysql.sys'
	);
# 有密码字符串哦 在其他实例执行 可直接创建出与本实例相同密码的用户。

5. Check the library or table size

# 查看整个实例占用空间大小：
SELECT
	concat( round( sum( data_length / 1024 / 1024 ), 2 ), 'MB' ) AS data_length_MB,
	concat( round( sum( index_length / 1024 / 1024 ), 2 ), 'MB' ) AS index_length_MB 
FROM
	information_schema.`TABLES`;
  
# 查看各个库占用大小：
SELECT
	TABLE_SCHEMA,
	concat( TRUNCATE ( sum( data_length )/ 1024 / 1024, 2 ), ' MB' ) AS data_size,
	concat( TRUNCATE ( sum( index_length )/ 1024 / 1024, 2 ), 'MB' ) AS index_size 
FROM
	information_schema.`TABLES`
GROUP BY
	TABLE_SCHEMA;
  
# 查看单个库占用空间大小：
SELECT
	concat( round( sum( data_length / 1024 / 1024 ), 2 ), 'MB' ) AS data_length_MB,
	concat( round( sum( index_length / 1024 / 1024 ), 2 ), 'MB' ) AS index_length_MB 
FROM
	information_schema.`TABLES`
WHERE
	table_schema = 'test_db';
  
# 查看单个表占用空间大小：
SELECT
	concat( round( sum( data_length / 1024 / 1024 ), 2 ), 'MB' ) AS data_length_MB,
	concat( round( sum( index_length / 1024 / 1024 ), 2 ), 'MB' ) AS index_length_MB 
FROM
	information_schema.`TABLES`
WHERE
	table_schema = 'test_db' 
	AND table_name = 'tbname';

6. Check table fragmentation and shrink statements

# 查看某个库下所有表的碎片情况：
SELECT
	t.TABLE_SCHEMA,
	t.TABLE_NAME,
	t.TABLE_ROWS,
	concat( round( t.DATA_LENGTH / 1024 / 1024, 2 ), 'M' ) AS size,
	t.INDEX_LENGTH,
	concat( round( t.DATA_FREE / 1024 / 1024, 2 ), 'M' ) AS datafree 
FROM
	information_schema.`TABLES` t 
WHERE
	t.TABLE_SCHEMA = 'test_db' 
ORDER BY
	datafree DESC;
  
# 收缩表，减少碎片：
alter table tb_name engine = innodb;
optimize table tb_name;

7. Find tables without primary keys

# 查找某一个库无主键表：
SELECT
table_schema,
table_name
FROM
    information_schema.`TABLES`
WHERE
    table_schema = 'test_db'
AND TABLE_NAME NOT IN (
    SELECT
        table_name
    FROM
        information_schema.table_constraints t
    JOIN information_schema.key_column_usage k USING (
        constraint_name,
        table_schema,
        table_name
    )
    WHERE
        t.constraint_type = 'PRIMARY KEY'
    AND t.table_schema = 'test_db'
);

# 查找除系统库外 无主键表：
SELECT
	t1.table_schema,
	t1.table_name
FROM
	information_schema.`TABLES` t1
LEFT OUTER JOIN information_schema.TABLE_CONSTRAINTS t2 ON t1.table_schema = t2.TABLE_SCHEMA
AND t1.table_name = t2.TABLE_NAME
AND t2.CONSTRAINT_NAME IN ('PRIMARY')
WHERE
	t2.table_name IS NULL
AND t1.TABLE_SCHEMA NOT IN (
	'information_schema',
	'performance_schema',
	'mysql',
	'sys'
) ;