MySQL表类型存储引擎的选择

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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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