mysql> create user rudonx1@'%' identified by 'xxxxxxxx';Query OK, 0 rows affected (0.04 sec)mysql> select user,host,password_expired,password_last_changed,password_lifetime from mysql.user where ... mysql> show variables like 'default_password_lifetime';+---------------------------+-------+| Variable_name | Value |+---------------------------+-------+| default_password_lifetime ...
例如搜索字串 “last_name LIKE ‘a%’”,一个是建了索引,一个是没有索引,性能差了 4 倍左右。另外,你应该也需要知道什么样的搜索是不能使用正常的索引的。例如,当你需要在一篇大的文章中搜索一个词时,如: “WHERE post_content LIKE ‘%apple%’”,索引可能是没有意义的。你可能需要使用 MySQL 全文索引 或是自己做一个索引(比如说:搜索关键词或是 Tag 什么的)
mysql> select * from performance_schema.threads where processlist_id=3\G;*************************** 1. row *************************** THREAD_ID: 28 NAME: thread/sql/one_connection TYPE: FOREGROUND PROCESSLIST_ID: 3 PROCESSLIST_USER: root PROCESSLIST_HOST: localhost PROCESSLIST_DB: rudonxPROCESSLIST_COMMAND: Query PROCESSLIST_TIME: 0...
一个事务也可能因为长时间运行的事务/未提交的事务而阻塞(information_schema.innodb_trx query字段显示为NULL)。# 解决方案1.通过对 INNODB_TRX 表执行以下查询,查看当前正在运行的事务:```mysql> select ... waiting_query: update candidates set score=3 where id=1blocking_trx_id: 11359225blocking_thread: 1257043blocking_query: null1 row in set (0.04 sec)``` **注**:如果查询中的blocking_query显示...
一个事务也可能因为长时间运行的事务/未提交的事务而阻塞(information_schema.innodb_trx query字段显示为NULL)。# 解决方案1.通过对 INNODB_TRX 表执行以下查询,查看当前正在运行的事务:```mysql> select ... waiting_query: update candidates set score=3 where id=1blocking_trx_id: 11359225blocking_thread: 1257043blocking_query: null1 row in set (0.04 sec)``` **注**:如果查询中的blocking_query显示...
mysql> source /root/all_databases.sql```待导入完成之后,问题可以复现,进行如下检查,发现没有任何存储过程和函数:```sqlmysql> SHOW FUNCTION STATUS WHERE Db = 'sys';Empty set (0.01 sec)mysql> SHOW PROCEDURE STATUS WHERE Db = 'sys';Empty set (0.00 sec)mysql> SELECT COUNT(*) FROM mysql.proc;+----------+| COUNT(*) |+----------+| 0 |+----------+1 row in set (0.00 sec)mysql> selec...
/未提交的事务而阻塞(information_schema.innodb_trx query字段显示为NULL)。# 解决方案1.通过对 INNODB_TRX 表执行以下查询,查看当前正在运行的事务:````undefinedmysql> select * from information_schema.i... waiting_query: update candidates set score=3 where id=1blocking_trx_id: 11359225blocking_thread: 1257043blocking_query: null1 row in set (0.04 sec)```` **注**:如果查询中的blocking_query显示未...
mysql> SELECT ENGINE,concat( TABLE_SCHEMA, '.', TABLE_NAME ) AS table_name,round( DATA_LENGTH / 1024 / 1024, 2 ) AS data_length,round( INDEX_LENGTH / 1024 / 1024, 2 ) AS index_length,round( DATA_FREE / 1024 / 1024, 2 ) AS data_free,(data_free /(index_length + data_length )) AS frag_ratio FROM information_schema.TABLES WHERE DATA_FREE > 0 ORDER BY frag_ratio ASC LIMIT 2;+---...
mysql> SELECT ENGINE,concat( TABLE_SCHEMA, '.', TABLE_NAME ) AS table_name,round( DATA_LENGTH / 1024 / 1024, 2 ) AS data_length,round( INDEX_LENGTH / 1024 / 1024, 2 ) AS index_length,round( DATA_FREE / 1024 / 1024, 2 ) AS data_free,(data_free /(index_length + data_length )) AS frag_ratio FROM information_schema.TABLES WHERE DATA_FREE > 0 ORDER BY frag_ratio ASC LIMIT 2;+--------+--...
# 问题描述如何避免在 UPDATE 或者 DELETE 的时候,忘记加 WHERE 条件,导致对数据库的全表数据进行误操作。# 问题分析开启 MySQL 系统变量 sql_safe_updates ,可以捕获没有使用索引,没有使用 WHERE 语句,LIMIT 语句导致的大量的更新或者删除的的操作。# 场景模拟1. 开启会话级别的 sql_safe_updates```sqlMySQL [sbtest]> show variables like 'sql_safe_updates';+------------------+-------+| Variable_name | V...
本文介绍云数据库 MySQL 版性能测试所使用的测试模型。 测试模型表结构CREATE TABLE `sbtest` (`id` INTEGER UNSIGNED NOT NULL AUTO_INCREMENT,`k` INTEGER UNSIGNED DEFAULT '0' NOT NULL,`c` CHAR(120) DEFAULT... 具体执行语句和条数如下: 主键 SELECT 语句, 10 条: SELECT c FROM ${rand_table_name} where id=${rand_id};范围 SELECT 语句, 4 条: SELECT c FROM ${rand_table_name} WHERE id BETWEEN ${rand_id_start} AND $...
**MySQL分页语法**``` select * from table limit 0, 20 ```思考: 使用分页,上面提到的第2点,这些成本真的能降低... select id,m_id, name, identity_no, address, create_time, modify_time from t2 where id > #{last_id},create_time > #{last_create_time} order by creat...
# 问题描述MySQL 5.7 的 SQL Modes 对 SQL 的检查更加严格和规范,会出现一些 SQL 兼容性问题。# 问题分析具体常见的问题包含以下几个方面:## 1.SQL查询的字段不包含在GROUP BY 语句中(ONLY_FULL_GROUP_BY)如果**SELECT**的字段与**GROUP BY**的字段不匹配,那么就会报错如下:````undefinedMySQL [dbtest]> select min(update_time),name,id from tb_author group by name;ERROR 1055 (42000): Expression #3 of SELECT li...