数据库的创建和管理是构建可靠数据的关键,关系到所存储数据的安全与稳定。在 MySQL 这个强大的关系型数据库系统中,数据库的创建与管理需要精准的步骤和妥善的配置。下面,将深入探讨如何使用MySQL 来管理数据库,我们不仅关注了基础的语法操作,还涉及了一些潜在的问题及实践,从创建数据库、授予权限到处理数据库名称大小写问题,再到配置数据库的属性等,带你走进数据库管理的正式通道。
使用create database语句创建数据库,用户拥有create权限才能创建数据库。
-- 例子:创建dba用户,拥有创建数据库名称为db_x的权限mysql> create user 'dba'@'%' identified by 'dba';Query OK, 0 rows affected (0.00 sec)mysql> grant create on `db\__`.* to 'dba'@'%';Query OK, 0 rows affected (0.00 sec)
授权时可指定授权的数据库名称,使用*表示所有数据库,使用_匹配一个字符,使用%匹配任意数量的字符。使用反斜杠()对_和%进行转意。
使用刚刚创建的账号创建数据库
[root@box3 ~]# mysql -udba -pdba -h172.16.20.51Welcome to the MySQL monitor. Commands end with ; or \g.mysql> create database biz_db;ERROR 1044 (42000): Access denied for user 'dba'@'%' to database 'biz_db'mysql> create database db02;ERROR 1044 (42000): Access denied for user 'dba'@'%' to database 'db02'mysql> create database db_x;Query OK, 1 row affected (0.00 sec)mysql> create database db_y;Query OK, 1 row affected (0.00 sec)mysql> show databases;+--------------------+| Database |+--------------------+| information_schema || db_x || db_y |+--------------------+mysql> show grants;+----------------------------------------+| Grants for dba@% |+----------------------------------------+| GRANT USAGE ON *.* TO 'dba'@'%' || GRANT CREATE ON `db\__`.* TO 'dba'@'%' |+----------------------------------------+
创建数据库之后,会在datadir指定的路径创建数据库同名目录
mysql> show variables where variable_name in ('datadir');+---------------+-----------------+| Variable_name | Value |+---------------+-----------------+| datadir | /var/lib/mysql/ |[root@box1 mysql]# ls -ld /var/lib/mysql/db_*drwxr-x---. 2 mysql mysql 20 4月 6 22:53 /var/lib/mysql/db_xdrwxr-x---. 2 mysql mysql 20 4月 6 22:58 /var/lib/mysql/db_y
数据库名称是否区分大小写?这跟文件系统文件名是否区分大小写有关。
linux系统下(ext系统文件系统、xfs),文件名称区分大小写,默认lower_case_tables_names设置为0,mysql数据库名称区分大小写。
mysql> show variables like '%lower_case%';+------------------------+-------+| Variable_name | Value |+------------------------+-------+| lower_case_file_system | OFF || lower_case_table_names | 0 |+------------------------+-------+mysql> create database biz_db;Query OK, 1 row affected (0.00 sec)mysql> create database Biz_db;Query OK, 1 row affected (0.00 sec)mysql> show databases like '%iz%';+-----------------+| Database (%iz%) |+-----------------+| Biz_db || biz_db |+-----------------+mysql> use BIZ_DBERROR 1049 (42000): Unknown database 'BIZ_DB'mysql> use Biz_dbDatabase changed[root@box1 mysql]# ls -ld /var/lib/mysql/*iz_dbdrwxr-x---. 2 mysql mysql 20 4月 6 23:03 /var/lib/mysql/biz_dbdrwxr-x---. 2 mysql mysql 20 4月 6 23:03 /var/lib/mysql/Biz_db
lower_case_file_system是一个只读参数。会根据mysql所在文件系统的特性设置相应的值。
mysql> set global lower_case_file_system=ON;ERROR 1238 (HY000): Variable 'lower_case_file_system' is a read only variable
如果把lower_case_file_system配置到配置文件,实例会无法启动
[root@box1 mysql]# service mysqld restartRedirecting to /bin/systemctl restart mysqld.serviceJob for mysqld.service failed because the control process exited with error code. See "systemctl status mysqld.service" and "journalctl -xe" for details.2021-04-07T03:14:52.203804Z 0 [ERROR] unknown variable 'lower_case_file_system=ON'2021-04-07T03:16:09.587798Z 0 [ERROR] unknown option '--lower_case_file_system'2021-04-07T03:18:06.738497Z 0 [ERROR] unknown option '--lower-case-file-system'
如果参数lower_case_table_names设置为1,则数据库名称和表名不区分大小写。
mysql> show variables like '%lower_case%';+------------------------+-------+| Variable_name | Value |+------------------------+-------+| lower_case_file_system | OFF || lower_case_table_names | 1 |+------------------------+-------+2 rows in set (0.03 sec)mysql> create database USER_DB;Query OK, 1 row affected (0.01 sec)mysql> create database user_db;ERROR 1007 (HY000): Cant create database 'user_db'; database exists[root@box1 mysql]# ls -ld /var/lib/mysql/*dbdrwxr-x---. 2 mysql mysql 20 4月 7 01:35 /var/lib/mysql/user_db
注意事项
对已有的数据库实例修改lower_case_table_names参数,可能会出现问题。
1、lower_case_table_names从0改到1
将参数从0改成1,如果原来的数据库中存在大写的数据库名或表名,修改参数后将无法访问这些数据库和表。
mysql> show variables like '%lower%';+------------------------+-------+| Variable_name | Value |+------------------------+-------+| lower_case_file_system | OFF || lower_case_table_names | 1 |+------------------------+-------+mysql> show databases;+--------------------+| Database |+--------------------+| information_schema || ORDER_DB |mysql> use ORDER_DB;ERROR 1049 (42000): Unknown database 'order_db'
2、lower_case_table_names从1改到0
将参数从1改成0,则原先的库、表都是以小写方式存在。如果SQL语句中使用大写的方式访问这些库表,会报错。
mysql> show variables like '%lower%';+------------------------+-------+| Variable_name | Value |+------------------------+-------+| lower_case_file_system | OFF || lower_case_table_names | 0 |+------------------------+-------+2 rows in set (0.00 sec)mysql> show tables;+---------------+| Tables_in_db1 |+---------------+| tab |+---------------+1 row in set (0.00 sec)mysql> select * from Tab;ERROR 1146 (42S02): Table 'db1.Tab' doesnt existmysql> select * from tab;+------+------+| col | COL2 |+------+------+| tab | tab |+------+------+1 row in set (0.00 sec)
3、将数据库迁移到不同的环境时,如果新老环境的lower_case_table_names参数不一样,则有可能会发生问题。
比如windows和linux环境下,lower_case_table_names参数的默认值不一样,换操作系统时,可能会遇到问题。
4、建议将所有环境的lower_case_table_names参数都设置成1。 数据库名称、表的名称只使用小写字符。
关于windows
在windows系统中,文件名不区分大小写,默认lower_case_table_names也为1,对应的数据库也不区分大小写。
mysql> show variables like '%lower%';+------------------------+-------+| Variable_name | Value |+------------------------+-------+| lower_case_file_system | ON || lower_case_table_names | 1 |+------------------------+-------+2 rows in set, 1 warning (0.00 sec)mysql> create database biz_db;Query OK, 1 row affected (0.00 sec)mysql> create database Biz_db;ERROR 1007 (HY000): Cant create database 'biz_db'; database existsmysql> create database ORDER_DB;Query OK, 1 row affected (0.00 sec)mysql> show databases;+--------------------+| Database |+--------------------+| information_schema || biz_db || mysql || order_db || performance_schema || sys |+--------------------+
创建数据库时,可以指定数据库的默认字符集和排序规则。
mysql> create database db_0;Query OK, 1 row affected (0.00 sec)mysql> create database db_1 default charset utf8;Query OK, 1 row affected (0.00 sec)mysql> create database db_2 default charset utf8 collate utf8_bin;Query OK, 1 row affected (0.00 sec)mysql> show create database db_0;+----------+-----------------------------------------------------------------+| Database | Create Database |+----------+-----------------------------------------------------------------+| db_0 | CREATE DATABASE `db_0` /*!40100 DEFAULT CHARACTER SET latin1 */ |+----------+-----------------------------------------------------------------+1 row in set (0.00 sec)mysql> show create database db_1;+----------+---------------------------------------------------------------+| Database | Create Database |+----------+---------------------------------------------------------------+| db_1 | CREATE DATABASE `db_1` /*!40100 DEFAULT CHARACTER SET utf8 */ |+----------+---------------------------------------------------------------+1 row in set (0.00 sec)mysql> show create database db_2;+----------+--------------------------------------------------------------------------------+| Database | Create Database |+----------+--------------------------------------------------------------------------------+| db_2 | CREATE DATABASE `db_2` /*!40100 DEFAULT CHARACTER SET utf8 COLLATE utf8_bin */ |+----------+--------------------------------------------------------------------------------+
数据库的字符集和collate属性保存在数据库目录下的db.opt文件中(8.0版本的机制有所变化,不再有db.opt文件,元数据存储在系统表中,系统表的存储引擎为innodb)
[root@box1 mysql]# ls -l /var/lib/mysql/db_?/db.opt-rw-r-----. 1 mysql mysql 65 4月 7 02:07 /var/lib/mysql/db_0/db.opt-rw-r-----. 1 mysql mysql 61 4月 7 02:07 /var/lib/mysql/db_1/db.opt-rw-r-----. 1 mysql mysql 54 4月 7 02:07 /var/lib/mysql/db_2/db.opt[root@box1 mysql]# more /var/lib/mysql/db_?/db.opt::::::::::::::/var/lib/mysql/db_0/db.opt::::::::::::::default-character-set=latin1default-collation=latin1_swedish_ci::::::::::::::/var/lib/mysql/db_1/db.opt::::::::::::::default-character-set=utf8default-collation=utf8_general_ci::::::::::::::/var/lib/mysql/db_2/db.opt::::::::::::::default-character-set=utf8default-collation=utf8_bin
mysql建表时如果不指定字符集和collate,会使用所在数据库的默认字符集和collate。
建议创建数据库的时候 就指定数据库的字符集和collate。
1.切换当前数据库
在mysql client中,使用use命令切换当前数据库。
mysql> show databases;+--------------------+| Database |+--------------------+| db_0 || db_1 || db_2 |mysql> use db_0;Database changed
2.查看当前数据库
使用函数database()或schema()查看会话当前所在数据库
mysql> use mysql;Reading table information for completion of table and column namesYou can turn off this feature to get a quicker startup with -ADatabase changedmysql> select schema();+----------+| schema() |+----------+| mysql |+----------+1 row in set (0.00 sec)mysql> select database();+------------+| database() |+------------+| mysql |+------------+1 row in set (0.00 sec)
3.修改数据库默认属性
mysql> alter database db_0 default charset utf8;Query OK, 1 row affected (0.00 sec)mysql> show create database db_0;+----------+---------------------------------------------------------------+| Database | Create Database |+----------+---------------------------------------------------------------+| db_0 | CREATE DATABASE `db_0` /*!40100 DEFAULT CHARACTER SET utf8 */ |+----------+---------------------------------------------------------------+1 row in set (0.00 sec)mysql> alter database db_0 default collate utf8_bin;Query OK, 1 row affected (0.00 sec)mysql> show create database db_0;+----------+--------------------------------------------------------------------------------+| Database | Create Database |+----------+--------------------------------------------------------------------------------+| db_0 | CREATE DATABASE `db_0` /*!40100 DEFAULT CHARACTER SET utf8 COLLATE utf8_bin */ |+----------+--------------------------------------------------------------------------------+1 row in set (0.00 sec)mysql> alter database db_0 default collate latin1_bin;Query OK, 1 row affected (0.00 sec)mysql> show create database db_0;+----------+------------------------------------------------------------------------------------+| Database | Create Database |+----------+------------------------------------------------------------------------------------+| db_0 | CREATE DATABASE `db_0` /*!40100 DEFAULT CHARACTER SET latin1 COLLATE latin1_bin */ |+----------+------------------------------------------------------------------------------------+1 row in set (0.00 sec)
4.删除数据库
使用drop命令删除数据库。删除需要drop权限。经过测试,5.7.32版本,需要drop on .的权限才能成功执行drop database命令。
grant drop on *.* to 'dba'@'%';[root@box3 ~]# mysql -udba -pdba -h172.16.20.51mysql> drop database db_0;Query OK, 0 rows affected (0.00 sec)
账号有db_2的drop权限,但无法删除该数据库:
mysql> show grants;+----------------------------------------------+| Grants for dba@% |+----------------------------------------------+| GRANT USAGE ON *.* TO 'dba'@'%' || GRANT DELETE, DROP ON `mysql`.* TO 'dba'@'%' || GRANT CREATE ON `db\__`.* TO 'dba'@'%' || GRANT DROP ON `db_1`.* TO 'dba'@'%' || GRANT DROP ON `db_x`.* TO 'dba'@'%' || GRANT DROP ON `db_2`.* TO 'dba'@'%' |+----------------------------------------------+6 rows in set (0.00 sec)mysql> show databases;+--------------------+| Database |+--------------------+| information_schema || db_2 || mysql |+--------------------+3 rows in set (0.00 sec)mysql> drop database db_2;ERROR 1044 (42000): Access denied for user 'dba'@'%' to database 'db_2'
删除数据库是一项高危操作,生产环境下需要严格规范删除数据库的操作流程,以下是一些关键点需要注意:
1、权限控制:严格控制drop database的权限,确保只有授权人员能够执行这一操作。
2、递归删除:drop database会递归删除数据库内的所有对象,包括表、视图等。执行前需确认清楚删除的对象。
3、性能影响:在数据库内有大量表或表占用大量空间时,drop database可能对数据库实例性能产生负面影响,影响正常业务访问。需在低峰期执行,或者考虑分阶段删除。
4、误删除恢复:误删除后的恢复比较耗时,因此在执行drop database前,应该经过仔细确认和备份,以减少误操作的可能性。
5、备份策略:始终确保有可靠的数据库备份。如果没有备份,误删除可能导致数据无法恢复。
更多技术信息请查看云掣官网云掣YunChe - 可观测运维专家 | 大数据运维托管 | 云MSP服务