元数据获取
除了数据行其他的类属性表属性都属于元数据，存放在InnoDB引擎的Inode中，一个Inode就是代表一个数据段。.
元素据是被保护起来的，是无法被直接操作的,但可以通过专用的视图以及命令对元数据进行查询。
参考资料: mysql体系结构
什么是视图
在这里，视频中视图相当于封装了一段sql语句，方便以后查询。
mysql> select teacher.tname,course.cname,student.sname,score.score
-> from student
-> join score
-> on student.sno=score.sno
-> join course
-> on score.cno=course.cno
-> join teacher
-> on course.tno=teacher.tno
-> where teacher.tname='oldguo'
-> having score.score < 60;
+--------+-------+-------+-------+
| tname | cname | sname | score |
+--------+-------+-------+-------+
| oldguo | mysql | li4 | 40 |
| oldguo | mysql | zh4 | 40 |
+--------+-------+-------+-------+
2 rows in set (0.00 sec)
#创建一个名为check_score的视图
mysql> create view check_score as select teacher.tname,course.cname,student.sname,score.score
-> from student
-> join score
-> on student.sno=score.sno
-> join course
-> on score.cno=course.cno
-> join teacher
-> on course.tno=teacher.tno
-> where teacher.tname='oldguo'
-> having score.score < 60;
Query OK, 0 rows affected (0.00 sec)
#使用check_score视图
mysql> select * from check_score;
+--------+-------+-------+-------+
| tname | cname | sname | score |
+--------+-------+-------+-------+
| oldguo | mysql | li4 | 40 |
| oldguo | mysql | zh4 | 40 |
+--------+-------+-------+-------+
2 rows in set (0.00 sec)
参考资料: 什么是视图
information_schema库
该库保存了大量的对元数据进行查询的视图，视图相当于是虚拟的表。
例如其中常用的表tables保存了所有数据库的名字以及表名
mysql> use information_schema;
mysql> show tables;
+---------------------------------------+
| Tables_in_information_schema |
+---------------------------------------+
| CHARACTER_SETS |
| COLLATIONS |
| COLLATION_CHARACTER_SET_APPLICABILITY |
| COLUMNS |
| COLUMN_PRIVILEGES |
| ENGINES |
| EVENTS |
| FILES |
| GLOBAL_STATUS |
| GLOBAL_VARIABLES |
| KEY_COLUMN_USAGE |
| OPTIMIZER_TRACE |
| PARAMETERS |
| PARTITIONS |
| PLUGINS |
| PROCESSLIST |
| PROFILING |
| REFERENTIAL_CONSTRAINTS |
| ROUTINES |
| SCHEMATA |
| SCHEMA_PRIVILEGES |
| SESSION_STATUS |
| SESSION_VARIABLES |
| STATISTICS |
| TABLES |
| TABLESPACES |
| TABLE_CONSTRAINTS |
| TABLE_PRIVILEGES |
| TRIGGERS |
| USER_PRIVILEGES |
| VIEWS |
| INNODB_LOCKS |
| INNODB_TRX |
| INNODB_SYS_DATAFILES |
| INNODB_FT_CONFIG |
| INNODB_SYS_VIRTUAL |
| INNODB_CMP |
| INNODB_FT_BEING_DELETED |
| INNODB_CMP_RESET |
| INNODB_CMP_PER_INDEX |
| INNODB_CMPMEM_RESET |
| INNODB_FT_DELETED |
| INNODB_BUFFER_PAGE_LRU |
| INNODB_LOCK_WAITS |
| INNODB_TEMP_TABLE_INFO |
| INNODB_SYS_INDEXES |
| INNODB_SYS_TABLES |
| INNODB_SYS_FIELDS |
| INNODB_CMP_PER_INDEX_RESET |
| INNODB_BUFFER_PAGE |
| INNODB_FT_DEFAULT_STOPWORD |
| INNODB_FT_INDEX_TABLE |
| INNODB_FT_INDEX_CACHE |
| INNODB_SYS_TABLESPACES |
| INNODB_METRICS |
| INNODB_SYS_FOREIGN_COLS |
| INNODB_CMPMEM |
| INNODB_BUFFER_POOL_STATS |
| INNODB_SYS_COLUMNS |
| INNODB_SYS_FOREIGN |
| INNODB_SYS_TABLESTATS |
+---------------------------------------+
61 rows in set (0.00 sec)
#查看tables表结构
mysql> desc tables;
+-----------------+---------------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-----------------+---------------------+------+-----+---------+-------+
| TABLE_CATALOG | varchar(512) | NO | | | |
| TABLE_SCHEMA | varchar(64) | NO | | | |
| TABLE_NAME | varchar(64) | NO | | | |
| TABLE_TYPE | varchar(64) | NO | | | |
| ENGINE | varchar(64) | YES | | NULL | |
| VERSION | bigint(21) unsigned | YES | | NULL | |
| ROW_FORMAT | varchar(10) | YES | | NULL | |
| TABLE_ROWS | bigint(21) unsigned | YES | | NULL | |
| AVG_ROW_LENGTH | bigint(21) unsigned | YES | | NULL | |
| DATA_LENGTH | bigint(21) unsigned | YES | | NULL | |
| MAX_DATA_LENGTH | bigint(21) unsigned | YES | | NULL | |
| INDEX_LENGTH | bigint(21) unsigned | YES | | NULL | |
| DATA_FREE | bigint(21) unsigned | YES | | NULL | |
| AUTO_INCREMENT | bigint(21) unsigned | YES | | NULL | |
| CREATE_TIME | datetime | YES | | NULL | |
| UPDATE_TIME | datetime | YES | | NULL | |
| CHECK_TIME | datetime | YES | | NULL | |
| TABLE_COLLATION | varchar(32) | YES | | NULL | |
| CHECKSUM | bigint(21) unsigned | YES | | NULL | |
| CREATE_OPTIONS | varchar(255) | YES | | NULL | |
| TABLE_COMMENT | varchar(2048) | NO | | | |
+-----------------+---------------------+------+-----+---------+-------+
21 rows in set (0.01 sec)
常用的表为TABLES
常用的列如下所示
TABLE_SCHEMA #表所在的库名
TABLE_NAME #表名
ENGINE #存储引擎
TABLE_ROWS #数据行
AVG_ROW_LENGTH #平均行长度
INDEX_LENGTH #索引长度
案例
#查看所有数据库的表名
mysql> select table_schema,table_name from information_schema.tables;
#仅显示部分
+--------------------+------------------------------------------------------+
| table_schema | table_name |
+--------------------+------------------------------------------------------+
| school | check_score |
| school | course |
| school | score |
| school | student |
| school | teacher |
| school | test |
+--------------------+------------------------------------------------------+
#一行显示每个数据库的表名
select table_schema,GROUP_CONCAT(table_name) as tables
from information_schema.tables
group by table_schema;
#查询所有innodb引擎的表
select table_schema,table_name,engine
from information_schema.tables
where ENGINE='innodb';
#统计school数据库中course表占用空间大小
#公式：平均行长度*行数+索引长度
select table_name,concat(((avg_row_length*table_rows+index_length)/1024),'kb') as size
from information_schema.tables
where table_schema='school' and table_name='course';
+------------+-----------+
| table_name | size |
+------------+-----------+
| course | 15.9990kb |
+------------+-----------+
1 row in set (0.00 sec)
#求school库所有表总大小
select table_schema,concat((sum(avg_row_length*table_rows+index_length)/1024),'kb') as size
from information_schema.tables
where table_schema='school' ;
+--------------+-----------+
| table_schema | size |
+--------------+-----------+
| school | 79.9814kb |
+--------------+-----------+
1 row in set (0.00 sec)
#统计每个数据库的大小，并从大到小排序
select table_schema,concat((sum(avg_row_length*table_rows+index_length)/1024),'kb') as size
from information_schema.tables
group by table_schema
order by size desc;
+--------------------+-------------+
| table_schema | size |
+--------------------+-------------+
| school | 79.9814kb |
| mysql | 2307.5078kb |
| sys | 15.9961kb |
| performance_schema | 0.0000kb |
| information_schema | NULL |
+--------------------+-------------+
5 rows in set (6.15 sec)
#注意information_schema是一个虚拟库所以不占空间，每次数据库启动就会自动生成。
对数据库进行备份
可使用mysqldump工具对mysql数据库进行备份
#对school数据库中的student表进行备份
mysqldump -uroot -p123 school student >/bak/school_student.sql
#concat拼接语句如下
select concat("mysqldump -uroot -p123 ",table_schema," ",table_name
," >/bak/",table_schema,"_",table_name,".sql")
from information_schema.tables;
#仅备份school库所有表
select concat("mysqldump -uroot -p123 ",table_schema," ",table_name
," >/bak/",table_schema,"_",table_name,".sql")
from information_schema.tables
where information_schema.tables.TABLE_SCHEMA='school';
+----------------------------------------------------------------------------------+
| concat("mysqldump -uroot -p123 ",table_schema," ",table_name
," >/bak/",table_schema,"_",table_name,".sql") |
+----------------------------------------------------------------------------------+
| mysqldump -uroot -p123 school check_score >/bak/school_check_score.sql |
| mysqldump -uroot -p123 school course >/bak/school_course.sql |
| mysqldump -uroot -p123 school score >/bak/school_score.sql |
| mysqldump -uroot -p123 school student >/bak/school_student.sql |
| mysqldump -uroot -p123 school teacher >/bak/school_teacher.sql |
| mysqldump -uroot -p123 school test >/bak/school_test.sql |
+----------------------------------------------------------------------------------+
6 rows in set (0.00 sec)
使用show命令
#查看帮助
mysql> help show;
#常用的show命令
show databases; #查看数据库名
show tables; #查看表名
show create database xx; #查看建库语句
show create table table_name; #查看建表语句
show processlist; #查看所有用户连接情况
show charset; #查看支持的字符集
show collation; #查看所有支持的校对规则
show grants for root; #查看用户的权限信息
show variables like '%xx%' #查看参数信息
show engines; #查看所有支持的存储引擎类型
show index from table_name; #查看表的索引信息
show engine innodb statusG; #查看innoDB引擎详细状态信息
show binary logs; #查看二进制日志的列表信息
show binlog events in '日志文件名'; #查看二进制日志的事件信息
show master status; #查看mysql当前使用二进制日志信息
show slave statusG; #查看从库状态信息
show relaylog events in '日志文件名'; #查看中继日志的事件信息
show status like ''; #查看数据库整体状态信息
将sql导出保存为文件
在mysql中可以将sql语句导出到文件中，但mysql会检查导出目录的安全性，需要在配置文件中设置安全目录路径
修改配置文件，设置安全目录
$ vim /etc/my.cnf
[mysqld]
#可以为空，表示可以导出到任何目录中
secure-file-priv=
使用concat连接sql语句导出到文件
mysql> select concat("alter table ",table_schema," ",table_name," discard tablespace;")
from information_schema.tables where table_schema='world'
into outfile '/tmp/world.sql'
#应用
mysql> source /tmp/world.sql
导出数据到文件
#数据一般使用excle表格式,csv或者xlsx格式
mysql> select * from city into outfile '/tmp/city.xlsx';
学习来自：郭老师博客，老男孩深标DBA课程 第三章