平凡

transaction isolation1. RU(read uncommitted)2. RC(read committed)3. RR(repeatable read)4. Serializablemysql提供了两种读取方式：快照度(snapshot read)和当前读(current read)current read包含三种情况：1. select ... lock in share mode 加S锁2. select ... for upd...

select a.DIGEST_TEXT as query, a.COUNT_STAR as exec_count, sec_to_time(a.SUM_TIMER_WAIT/1000000000000) as exec_time_total, sec_to_time(a.MAX_TIMER_WAIT/1000000000000) as exec_time_max, (a.AVG_TIMER_WAIT/1000000000) as exec_time_avg_ms, a.SUM_ROWS_SENT as r

1. 表t_test中的age字段有普通索引create table t_test(id int not null, name varchar(32), age int, index(age)) ;2. 根据age字段查询数据select * from t_test where age < 20;问题及解析：该查询不一定走索引，和表的数据量有关系，只有在满足条件的数据占比较小时（占全部数据的比例）才会走索引...

表约束信息INFORMATION_SCHEMA NameSHOW NameRemarksCONSTRAINT_CATALOG defCONSTRAINT_SCHEMA  CONSTRAINT_NAME  TABLE_SCHEMA

表权限The TABLE_PRIVILEGES table provides information about table privileges. This information comes from the mysql.tables_priv grant table.INFORMATION_SCHEMA NameSHOW NameR

触发器The TRIGGERS table provides information about triggers. To see information about a table's triggers, you must have the TRIGGER privilege for the table.INFORMATION_SCHEMA Name

用户权限The USER_PRIVILEGES table provides information about global privileges. This information comes from the mysql.user grant table.INFORMATION_SCHEMA NameSHOW NameRemarks

1.timestamp存储和时区相关，即会根据时区做转换如：+8时区存进去， 而在+9时区取出，则时间为+9时区的时间而datetime存储和时区不相关，不会做转换如：+8时区存进去，在+9时区取出时，仍为+8时区的时间2.占用空间不一样，前者4字节，后者8字节 例子：create table t_timezone ( ts timestamp, dt datetime...

### Cause: java.sql.SQLException: The table 'xxx' is full; uncategorized SQLException; SQL state [HY000]; error code [1114]; The table 'xxx' is full; nested exception is java.sql.SQLException: The ta...

mysql 5.71.grant all privileges on *.* to 'username'@'%' identified by 'username123';select * from mysql.user;localhostrootlocalhostmysql.sys%usernamemysql81.create user 'usernam...

default_authentication_pluginshow variables 'default_authentication_plugin';mysql 5.7: mysql_native_passwordmysql8: caching_sha2_password1.alter user authentication pluginalter user '...

updated variable still take effect after mysql restart./var/lib/mysql/mysqld-autto.cnf;set persist password_require_current=on

表空间信息，该表不包含innodb表空间，INNODB_SYS_TABLESPACESand INNODB_SYS_DATAFILES从5.7.8开始，innodb表空间信息查看INFORMATION_SCHEMA.FILESThe TABLESPACES table provides information about active tablespaces.

数据库中的表信息The TABLES table provides information about tables in databases.INFORMATION_SCHEMA NameSHOW NameRemarksTABLE_CATALOG defTABLE_SCHEMA

该表包含每个字符集的所有信息 The COLLATIONS table provides information about collations for each character set.INFORMATION_SCHEMA NameSHOW NameRemarksCOLLATION_NAMEColl

该表描述了字符集适合哪种比对方法The COLLATION_CHARACTER_SET_APPLICABILITY table indicates what character set is applicable for what collation. The columns are equivalent to the first two display fields that we ge

该系统表包含了所有表的列信息The COLUMNS table provides information about columns in tables.INFORMATION_SCHEMA NameSHOW NameRemarksTABLE_CATALOG defTABLE_SCHEM

该表提供了有关列权限信息，这些信息来自mysql.columns_priv权限表The COLUMN_PRIVILEGES table provides information about column privileges. This information comes from the mysql.columns_priv grant table.I

存储引擎信息表The ENGINES table provides information about storage engines.INFORMATION_SCHEMA NameSHOW NameRemarksENGINEEngineMySQL extensionSUPPORT

调度计划事件信息表The EVENTS table provides information about scheduled events, which are discussed in Section 23.4, “Using the Event Scheduler”. The SHOW Name values correspond to column names of the 

包含了表空间数据存储的文件The FILES table provides information about the files in which MySQL tablespace data is stored.INFORMATION_SCHEMA.FILES provides information about InnoDB data files. In NDB C

NoteAs of MySQL 5.7.6, the value of the show_compatibility_56 system variable affects the information available from the tables described here. For details, see the description of that variable

进程列表The PROCESSLIST table provides information about which threads are running.INFORMATION_SCHEMA NameSHOW NameRemarksIDIdMySQL extensionUSER

该表包含了可用的字符集The CHARACTER_SETS table provides information about available character sets.INFORMATION_SCHEMA NameSHOW NameRemarksCHARACTER_SET_NAMECharset