麒麟v10 上部署 TiDB v5.1.2 生产环境优化实践
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2023-05-14
常用SQL语句分享
前言:
日常工作或学习过程中,我们可能会经常用到某些SQL,建议大家多多整理记录下这些常用的SQL,这样后续用到会方便很多。笔者在工作及学习过程中也整理了下个人常用的SQL,现在分享给你!可能有些SQL你还不常用,但还是希望对你有所帮助,说不定某日有需求就可以用到。
注:下文分享的SQL适用于MySQL 5.7 版本,低版本可能稍许不同。有些SQL可能执行需要较高权限。
1.show相关语句
2.查看账户相关信息
# 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数据库链接
# 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.拼接创建数据库或用户语句
# 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.查看库或表大小
# 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.查看表碎片及收缩语句
# 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.查找无主键表
# 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' ) ;
总结:
希望这些SQL语句能对你有所帮助,可以收藏一下,说不定某次就用到了呢!
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