1、查看当前数据库支出的存储引擎
方法1：
mysql> show engines \G;
*************************** 1. row ***************************
Engine: InnoDB
Support: YES
Comment: Supports transactions, row-level locking, and foreign keys
Transactions: YES
XA: YES
Savepoints: YES
*************************** 2. row ***************************
Engine: MRG_MYISAM
Support: YES
Comment: Collection of identical MyISAM tables
Transactions: NO
XA: NO
Savepoints: NO
*************************** 3. row ***************************
Engine: MEMORY
Support: YES
Comment: Hash based, stored in memory, useful for temporary tables
Transactions: NO
XA: NO
Savepoints: NO
*************************** 4. row ***************************
Engine: BLACKHOLE
Support: YES
Comment: /dev/null storage engine (anything you write to it disappears)
Transactions: NO
XA: NO
Savepoints: NO
*************************** 5. row ***************************
Engine: MyISAM
Support: DEFAULT
Comment: MyISAM storage engine
Transactions: NO
XA: NO
Savepoints: NO
*************************** 6. row ***************************
Engine: CSV
Support: YES
Comment: CSV storage engine
Transactions: NO
XA: NO
Savepoints: NO
*************************** 7. row ***************************
Engine: ARCHIVE
Support: YES
Comment: Archive storage engine
Transactions: NO
XA: NO
Savepoints: NO
*************************** 8. row ***************************
Engine: PERFORMANCE_SCHEMA
Support: YES
Comment: Performance Schema
Transactions: NO
XA: NO
Savepoints: NO
*************************** 9. row ***************************
Engine: FEDERATED
Support: NO
Comment: Federated MySQL storage engine
Transactions: NULL
XA: NULL
Savepoints: NULL
9 rows in set (0.00 sec)
ERROR:
No query specified
方法2：
（Value 显示为“DISABLED”的记录表示支持该存储引擎，但是数据库启动的时候被禁用。）
mysql> show variables like 'have%';
+------------------------+----------+
| Variable_name | Value |
+------------------------+----------+
| have_compress | YES |
| have_crypt | NO |
| have_dynamic_loading | YES |
| have_geometry | YES |
| have_openssl | DISABLED |
| have_profiling | YES |
| have_query_cache | YES |
| have_rtree_keys | YES |
| have_ssl | DISABLED |
| have_statement_timeout | YES |
| have_symlink | YES |
+------------------------+----------+
11 rows in set, 1 warning (0.00 sec)
2、ENGINE={存储引起类型} 创建表的时候，设置存储引擎
mysql> create table a(
-> i bigint(20) not null auto_increment,
-> primary key (i)
-> ) engine=myisam default charset=gbk;
ERROR 2006 (HY000): MySQL server has gone away
No connection. Trying to reconnect...
Connection id: 3
Current database: test
Query OK, 0 rows affected (1.33 sec)
3、alter able tablename engine={存储引起类型} 修改表为其他存储引擎
mysql> alter table a engine=innodb;
Query OK, 0 rows affected (1.70 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> show create table a \G;
*************************** 1. row ***************************
Table: a
Create Table: CREATE TABLE `a` (
`i` bigint(20) NOT NULL AUTO_INCREMENT,
PRIMARY KEY (`i`)
) ENGINE=InnoDB DEFAULT CHARSET=gbk
1 row in set (0.14 sec)
3.1 常用存储引擎的对比
| 特点 | MyISAM | InnoDB | MEMORY | MERGE | NDB |
| 存储限制 | 有 | 64TB | 有 | 没有 | 有 |
| 事务安全 | 支持 | ||||
| 锁机制 | 表锁 | 行锁 | 表锁 | 表锁 | 表锁 |
| B 树索引 | 支持 | 支持 | 支持 | 支持 | 支持 |
| 哈希索引 | 支持 | 支持 | |||
| 全文索引 | 支持 | ||||
| 集群索引 | 支持 | ||||
| 数据缓存 | 支持 | 支持 | 支持 | ||
| 索引缓存 | 支持 | 支持 | 支持 | 支持 | 支持 |
| 数据可压缩 | 支持 | ||||
| 空间使用 | 低 | 高 | N/A | 低 | 低 |
| 内存使用 | 低 | 高 | 中等 | 低 | 高 |
| 批量插入的速度 | 高 | 低 | 高 | 高 | 高 |
| 支持外键 | 支持 |
3.2 常用存储引擎学习（MyISAM、InnoDB、MEMORY 和 MERGE）
MyISAM：
默认的MySQL存储引擎，不支持事务和外键
优点：访问速度快
每个MyISAM在磁盘上存储成3个文件，其文件名和表名都相同。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。)
InnoDB:
处理效率较差，占用较多的空间用来保留数据和索引
优点：具有提交、回滚、奔溃恢复能力的事务安全、唯一支持外键的存储引擎
自动增长列：InnoDB 表的自动增长列可以手工插入，但是插入的值如果是空或者 0，则实际插入的将是自动增长后的值
mysql> create table autoincre_demo(
-> i smallint not null auto_increment,
-> name varchar(10),primary key(i)
-> )engine=innodb;
ERROR 2006 (HY000): MySQL server has gone away
No connection. Trying to reconnect...
Connection id: 5
Current database: test
Query OK, 0 rows affected (1.19 sec)
mysql> insert into autoincre_demo values(1,"121"),(0,"dddf"),(null,"fdf");
Query OK, 3 rows affected (0.59 sec)
Records: 3 Duplicates: 0 Warnings: 0
mysql> select * from autoincre_demo;
+---+------+
| i | name |
+---+------+
| 1 | 121 |
| 2 | dddf |
| 3 | fdf |
+---+------+
3 rows in set (0.00 sec)
alter table tabename auto_increment=n 设置自动增长列的初始值（此值默认从1开始）
可以使用 LAST_INSERT_ID()查询当前线程最后插入记录使用的值。如果一次插入了多条记录，那么返回的是第一条记录使用的自动增长值。
下面的例子演示了使用 LAST_INSERT_ID()的情况：
mysql> insert into autoincre_demo(name) values('3');
Query OK, 1 row affected (0.36 sec)
mysql> select LAST_INSERT_ID();
+------------------+
| LAST_INSERT_ID() |
+------------------+
| 15 |
+------------------+
1 row in set (0.00 sec)
mysql> insert into autoincre_demo(name) values('3'),('6'),('323'),('21');
Query OK, 4 rows affected (0.09 sec)
Records: 4 Duplicates: 0 Warnings: 0
mysql> select LAST_INSERT_ID();
+------------------+
| LAST_INSERT_ID() |
+------------------+
| 16 |
+------------------+
1 row in set (0.00 sec)
外键约束：
在创建外键的时候，要求父表必须有对应的索引，子表在创建外键的时候也会自动创建对应的索引。
下面是样例数据库中的两个表，country 表是父表，country_id 为主键索引，city 表是子表，country_id 字段对 country 表的 country_id 有外键。
mysql> create table country(
-> country_id smallint unsigned not null auto_increment,
-> country varchar(50) not null,
-> last_update timestamp not null default current_timestamp on update current_timestamp,
-> primary key(country_id)
-> )engine=innodb default charset=utf8;
Query OK, 0 rows affected (0.86 sec)
mysql> CREATE TABLE city (
-> city_id SMALLINT UNSIGNED NOT NULL AUTO_INCREMENT,
-> city VARCHAR(50) NOT NULL,
-> country_id SMALLINT UNSIGNED NOT NULL,
-> last_update TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
-> PRIMARY KEY (city_id),
-> KEY idx_fk_country_id (country_id),
-> CONSTRAINT `fk_city_country` FOREIGN KEY (country_id) REFERENCES country (country_id) ON
-> DELETE RESTRICT ON UPDATE CASCADE
-> )ENGINE=InnoDB DEFAULT CHARSET=utf8;
Query OK, 0 rows affected (3.22 sec)
在创建索引的时候，可以指定在删除、更新父表时，对子表进行的相应操作，包 RESTRICT、CASCADE、SET NULL 和 NO ACTION
RESTRICT和NO ACTION相同，是指限制在子表有关联记录的情况下父表不能更新CASCADE表示父表在更新或者删除时，更新或者删除子表对应记录；SET NULL则表示父表在更新或者删除的时候，子表的对应字段被SET NULL。
mysql> select * from country;
+------------+---------+---------------------+
| country_id | country | last_update |
+------------+---------+---------------------+
| 1 | AAA | 2021-06-16 15:09:22 |
+------------+---------+---------------------+
1 row in set (0.00 sec)
mysql> select * from city;
+---------+------+------------+---------------------+
| city_id | city | country_id | last_update |
+---------+------+------------+---------------------+
| 10 | bb | 1 | 2021-06-16 15:11:45 |
+---------+------+------------+---------------------+
1 row in set (0.00 sec)
mysql> delete from country where country_id = 1;
ERROR 1451 (23000): Cannot delete or update a parent row: a foreign key constraint fails (`test`.`city`, CONSTRAINT `fk_city_country` FOREIGN KEY (`country_id`) REFERENCES `country` (`country_id`) ON UPDATE CASCADE)
mysql> update country set country_id = 10000 where country_id = 1;
Query OK, 1 row affected (0.62 sec)
Rows matched: 1 Changed: 1 Warnings: 0
mysql> select * from country;
+------------+---------+---------------------+
| country_id | country | last_update |
+------------+---------+---------------------+
| 10000 | AAA | 2021-06-16 15:13:35 |
+------------+---------+---------------------+
1 row in set (0.00 sec)
mysql> select * from city
-> ;
+---------+------+------------+---------------------+
| city_id | city | country_id | last_update |
+---------+------+------------+---------------------+
| 10 | bb | 10000 | 2021-06-16 15:11:45 |
+---------+------+------------+---------------------+
1 row in set (0.00 sec)
在导入多个表的数据时，如果需要忽略表之前的导入顺序，可以暂时关闭外键的检查；同样，在执行 LOAD DATA 和 ALTER TABLE 操作的时候，可以通过暂时关闭外键约束来加快处理的速度，关闭的命令是“SET FOREIGN_KEY_CHECKS = 0;”，执行完成之后，通过执行“SETFOREIGN_KEY_CHECKS = 1;”语句改回原状态。
查看表外键信息：show create table 或者 show table status 命令
mysql> show table status like 'city' \G;
*************************** 1. row ***************************
Name: city
Engine: InnoDB
Version: 10
Row_format: Dynamic
Rows: 1
Avg_row_length: 16384
Data_length: 16384
Max_data_length: 0
Index_length: 16384
Data_free: 0
Auto_increment: 11
Create_time: 2021-06-16 15:02:17
Update_time: 2021-06-16 15:13:35
Check_time: NULL
Collation: utf8_general_ci
Checksum: NULL
Create_options:
Comment:
1 row in set (0.43 sec)
ERROR:
No query specified
存储方式：
- （1）、使用共享表空间存储：表的表结构保存在.frm文件中，数据+索引存在
innodb_data_home_dir和innodb_data_file_path定义的表空间中，可以是多个文件 - （2）、使用多表空间存储：表的表结构也保存在.frm文件中，数据+索引单独存在.
ibd中；如果是分区表，则每个分区对应单独的.ibd文件，文件名是：“表名+分区名”，可以在创建分区的时候指定每个分区的数据文件的位置，以此来将表的 IO 均匀分布在多个磁盘上
MEMORY：
使用存在内存中的内容来创建表
每个 MEMORY 表只实际对应一个磁盘文件，格式是.frm。
优点：访问速度快（数据存储在内存中），并且默认使用HASH索引，服务关闭则数据丢失
mysql> CREATE TABLE tab_memory ENGINE=MEMORY
-> SELECT city_id,city,country_id
-> FROM city GROUP BY city_id;
ERROR 2006 (HY000): MySQL server has gone away
No connection. Trying to reconnect...
Connection id: 12
Current database: test
Query OK, 1 row affected (0.62 sec)
Records: 1 Duplicates: 0 Warnings: 0
mysql> select * from tab_memory;
+---------+------+------------+
| city_id | city | country_id |
+---------+------+------------+
| 10 | bb | 10000 |
+---------+------+------------+
1 row in set (0.00 sec)
mysql> show table status like 'tab_memory' \G
*************************** 1. row ***************************
Name: tab_memory
Engine: MEMORY
Version: 10
Row_format: Fixed
Rows: 1
Avg_row_length: 155
Data_length: 520320
Max_data_length: 65011650
Index_length: 0
Data_free: 0
Auto_increment: NULL
Create_time: 2021-06-16 15:28:58
Update_time: NULL
Check_time: NULL
Collation: utf8_unicode_ci
Checksum: NULL
Create_options:
Comment:
1 row in set (0.00 sec)
给表创建索引的时候可以指定索引类型是HASH或是BTREE
mysql> create index mem_hash using hash on tab_memory(city_id);
ERROR 2006 (HY000): MySQL server has gone away
No connection. Trying to reconnect...
Connection id: 13
Current database: test
Query OK, 1 row affected (0.63 sec)
Records: 1 Duplicates: 0 Warnings: 0
mysql> show index from tab_memory \G;
*************************** 1. row ***************************
Table: tab_memory
Non_unique: 1
Key_name: mem_hash
Seq_in_index: 1
Column_name: city_id
Collation: NULL
Cardinality: 1
Sub_part: NULL
Packed: NULL
Null:
Index_type: HASH
Comment:
Index_comment:
1 row in set (0.32 sec)
ERROR:
No query specified
mysql> drop index mem_hash on tab_memory;
Query OK, 1 row affected (0.31 sec)
Records: 1 Duplicates: 0 Warnings: 0
mysql> create index mem_hash using btree on tab_memory(city_id);
Query OK, 1 row affected (0.16 sec)
Records: 1 Duplicates: 0 Warnings: 0
mysql> show index from tab_memory \G;
*************************** 1. row ***************************
Table: tab_memory
Non_unique: 1
Key_name: mem_hash
Seq_in_index: 1
Column_name: city_id
Collation: A
Cardinality: NULL
Sub_part: NULL
Packed: NULL
Null:
Index_type: BTREE
Comment:
Index_comment:
1 row in set (0.00 sec)
ERROR:
No query specified
MERGE：
此存储殷勤是一组MyISAM表的组合
对 MERGE 类型的表可以进行查询、更新、删除的操作，这些操作实际上是对内部的实际的 MyISAM 表进行的。
对于 MERGE 类型表的插入操作，是通过INSERT_METHOD 子句定义插入的表，可以有 3 个不同的值，使用 FIRST 或 LAST 值使得插入操作被相应地作用在第一或最后一个表上，不定义这个子句或者定义为 NO，表示不能对这个 MERGE 表执行插入操作。
可以对 MERGE 表进行 DROP 操作，这个操作只是删除 MERGE 的定义，对内部的表没有任何的影响。
存储文件：一个.frm 文件存储表定义，另一个.MRG 文件包含组合表的信息，包括 MERGE 表由哪些表组成、插入新的数据时的依据
mysql> create table payment_2020(
-> country_id smallint,
-> payment_date datetime,
-> amount DECIMAL(15,2),
-> KEY idx_fk_country_id (country_id)
-> )engine=myisam;
Query OK, 0 rows affected (0.25 sec)
mysql> create table payment_2021(
-> country_id smallint,
-> payment_date datetime,
-> amount DECIMAL(15,2),
-> KEY idx_fk_country_id (country_id)
-> )engine=myisam;
Query OK, 0 rows affected (0.54 sec)
mysql> CREATE TABLE payment_all(
-> country_id smallint,
-> payment_date datetime,
-> amount DECIMAL(15,2),
-> INDEX(country_id)
-> )engine=merge union=(payment_2020,payment_2021) INSERT_METHOD=LAST;
Query OK, 0 rows affected (0.47 sec)
分别向2020和2021中插入数据，并查询
mysql> insert into payment_2020 values(1,'2020-06-01',100000),(2,'2020-06-15',150000);
Query OK, 2 rows affected (0.00 sec)
Records: 2 Duplicates: 0 Warnings: 0
mysql> insert into payment_2021 values(1,'2021-04-20',35000),(2,'2021-06-15',220000);
Query OK, 2 rows affected (0.03 sec)
Records: 2 Duplicates: 0 Warnings: 0
mysql> select * from payment_2020;
+------------+---------------------+-----------+
| country_id | payment_date | amount |
+------------+---------------------+-----------+
| 1 | 2020-06-01 00:00:00 | 100000.00 |
| 2 | 2020-06-15 00:00:00 | 150000.00 |
+------------+---------------------+-----------+
2 rows in set (0.00 sec)
mysql> select * from payment_2021;
+------------+---------------------+-----------+
| country_id | payment_date | amount |
+------------+---------------------+-----------+
| 1 | 2021-04-20 00:00:00 | 35000.00 |
| 2 | 2021-06-15 00:00:00 | 220000.00 |
+------------+---------------------+-----------+
2 rows in set (0.00 sec)
mysql> select * from payment_all;
+------------+---------------------+-----------+
| country_id | payment_date | amount |
+------------+---------------------+-----------+
| 1 | 2020-06-01 00:00:00 | 100000.00 |
| 2 | 2020-06-15 00:00:00 | 150000.00 |
| 1 | 2021-04-20 00:00:00 | 35000.00 |
| 2 | 2021-06-15 00:00:00 | 220000.00 |
+------------+---------------------+-----------+
4 rows in set (0.00 sec)
可以发现，payment_all 表中的数据是 payment_2020 和 payment_2021 表的记录合并后的结果集
下面向 MERGE 表插入一条记录，由于 MERGE 表的定义是 INSERT_METHOD=LAST，就会向最后一个表中插入记录，所以虽然这里插入的记录是 2006 年的，但仍然会写到 payment_2021表中。
mysql> insert into payment_all values(3,'2020-03-30',12333131);
Query OK, 1 row affected (0.31 sec)
mysql> select * from payment_all;
+------------+---------------------+-------------+
| country_id | payment_date | amount |
+------------+---------------------+-------------+
| 1 | 2020-06-01 00:00:00 | 100000.00 |
| 2 | 2020-06-15 00:00:00 | 150000.00 |
| 1 | 2021-04-20 00:00:00 | 35000.00 |
| 2 | 2021-06-15 00:00:00 | 220000.00 |
| 3 | 2020-03-30 00:00:00 | 12333131.00 |
+------------+---------------------+-------------+
5 rows in set (0.00 sec)
mysql> select * from payment_2021;
+------------+---------------------+-------------+
| country_id | payment_date | amount |
+------------+---------------------+-------------+
| 1 | 2021-04-20 00:00:00 | 35000.00 |
| 2 | 2021-06-15 00:00:00 | 220000.00 |
| 3 | 2020-03-30 00:00:00 | 12333131.00 |
+------------+---------------------+-------------+
3 rows in set (0.00 sec)
mysql> select * from payment_2020;
+------------+---------------------+-----------+
| country_id | payment_date | amount |
+------------+---------------------+-----------+
| 1 | 2020-06-01 00:00:00 | 100000.00 |
| 2 | 2020-06-15 00:00:00 | 150000.00 |
+------------+---------------------+-----------+
2 rows in set (0.00 sec)
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