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MySql 技巧小荔枝
在日常使用MySql的场景下,我个人比较少用到一些MySql特殊的命令,在这里记录下,以免以后用到的时候到处搜索资料.例子都已经经过本人实际测试,可以方心使用.
- 查询mysql版本
mysql> select version();
+-----------+
| version() |
+-----------+
| 8.0.11 |
+-----------+
1 row in set (0.00 sec)- 查看mysql当前支持的存储引擎
mysql> show engines;
+--------------------+---------+----------------------------------------------------------------+--------------+------+------------+
| Engine | Support | Comment | Transactions | XA | Savepoints |
+--------------------+---------+----------------------------------------------------------------+--------------+------+------------+
| FEDERATED | NO | Federated MySQL storage engine | NULL | NULL | NULL |
| MEMORY | YES | Hash based, stored in memory, useful for temporary tables | NO | NO | NO |
| InnoDB | DEFAULT | Supports transactions, row-level locking, and foreign keys | YES | YES | YES |
| PERFORMANCE_SCHEMA | YES | Performance Schema | NO | NO | NO |
| MyISAM | YES | MyISAM storage engine | NO | NO | NO |
| MRG_MYISAM | YES | Collection of identical MyISAM tables | NO | NO | NO |
| BLACKHOLE | YES | /dev/null storage engine (anything you write to it disappears) | NO | NO | NO |
| CSV | YES | CSV storage engine | NO | NO | NO |
| ARCHIVE | YES | Archive storage engine | NO | NO | NO |
+--------------------+---------+----------------------------------------------------------------+--------------+------+------------+
9 rows in set (0.00 sec)
Mysql数据库存储引擎有什么区别？
mysql的存储引擎包括：MyISAM、InnoDB、BDB、MEMORY、MERGE、EXAMPLE、NDBCluster、ARCHIVE、CSV、BLACKHOLE、FEDERATED等,其中InnoDB和BDB提供事务安全表，其他存储引擎都是非事务安全表。
最常使用的2种存储引擎:
1. MyISAM是Mysql的早期版本的默认存储引擎,从MySQL5.5.5以后,InnoDB是默认引擎。在早期版本中,当create创建新表时，未指定新表的存储引擎时，默认使用MyISAM。每个MyISAM在磁盘上存储成三个文件。文件名都和表名相同，扩展名分别是.frm（存储表定义）、.MYD(MYData，存储数据)、.MYI(MYIndex，存储索引)。数据文件和索引文件可以放置在不同的目录，平均分布io，获得更快的速度。
2. InnoDB存储引擎提供了具有提交、回滚和崩溃恢复能力的事务安全,是后来新版本的默认引擎,这你可以看到我下面的例子(查看mysql当前默认的存储引擎)中验证。但是对比MyISAM的存储引擎，InnoDB写的处理效率差一些并且会占用更多的磁盘空间以保留数据和索引。
- 要看某个表用了什么引擎(在显示结果里参数engine后面的就表示该表当前用的存储引擎)
mysql> show create table students;
+----------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table |
+----------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| students | CREATE TABLE `students` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`name` varchar(32) NOT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=6 DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci |
+----------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)或者show table status from db_name where name='table_name'; 也可以
mysql> show table status from think_db where name='students';
+----------+--------+---------+------------+------+----------------+-------------+-----------------+--------------+-----------+----------------+---------------------+---------------------+------------+--------------------+----------+----------------+---------+
| Name | Engine | Version | Row_format | Rows | Avg_row_length | Data_length | Max_data_length | Index_length | Data_free | Auto_increment | Create_time | Update_time | Check_time | Collation | Checksum | Create_options | Comment |
+----------+--------+---------+------------+------+----------------+-------------+-----------------+--------------+-----------+----------------+---------------------+---------------------+------------+--------------------+----------+----------------+---------+
| students | InnoDB | 10 | Dynamic | 5 | 3276 | 16384 | 0 | 0 | 0 | 6 | 2018-07-09 16:37:20 | 2018-07-09 16:59:46 | NULL | utf8mb4_0900_ai_ci | NULL | | |
+----------+--------+---------+------------+------+----------------+-------------+-----------------+--------------+-----------+----------------+---------------------+---------------------+------------+--------------------+----------+----------------+---------+
1 row in set (0.06 sec)
- 查看mysql当前默认的存储引擎
mysql> show variables like '%storage_engine%';
+----------------------------------+-----------+
| Variable_name | Value |
+----------------------------------+-----------+
| default_storage_engine | InnoDB |
| default_tmp_storage_engine | InnoDB |
| disabled_storage_engines | |
| internal_tmp_disk_storage_engine | InnoDB |
| internal_tmp_mem_storage_engine | TempTable |
+----------------------------------+-----------+
5 rows in set (0.01 sec)
- 修改表引擎
格式: alter table table_name engine=engine_name;
mysql> alter table students engine=innodb;
Query OK, 0 rows affected (0.20 sec)
Records: 0 Duplicates: 0 Warnings: 0