What is a partition table? What is a temporary table? The following article will take you through the partition tables and temporary tables in MySQL. I hope it will be helpful to you!
There is a kind of table in MySQL called a temporary table, which refers to using CREATE TEMPORARY TABLE## Created by the # statement, it is a special type of table that allows the storage of temporary results, which can be reused multiple times in a single session and is invisible to other connections. When the connection is interrupted, the data table will be lost, but You can also use DROP TABLE to explicitly delete it if you don't need it. [Related recommendations: mysql video tutorial]
CREATE TEMPORARY TABLE table_name( column_1_definition, column_2_definition, .... );
CREATE TEMPORARY TABLE statement. If you are in trouble, you can use the following statement
CREATE TEMPORARY TABLE temp_table_name SELECT * FROM table_name LIMIT 0;
Example of creating a temporary table
Create a new temporary table named tblemployee. This table cannot be seen using SHOW TABLES. of.create temporary table tblemployee ( id int auto_increment Primary key, emp_name varchar(500), emp_address varchar(500), emp_dept_id int )
mysql> insert into tblemployee values(1,'张三','北京',2); Query OK, 1 row affected (0.00 sec) mysql> select * from tblemployee; +----+----------+-------------+-------------+ | id | emp_name | emp_address | emp_dept_id | +----+----------+-------------+-------------+ | 1 | 张三 | 北京 | 2 | +----+----------+-------------+-------------+ 1 row in set (0.01 sec) mysql>
Create based on existing table structure
First create two tables.
create table tb_user(user_name varchar(255),user_id int(11));
insert tb_user values("张三",1);
insert tb_user values("李四",2);
insert tb_user values("王五",3);
create table balance(user_id int(11),balance decimal(5,2));
insert balance values(1,200);
insert balance values(2,150);
insert balance values(3,100);create temporary table temp_user_balance select user_name,balance from tb_user left join balance on tb_user.user_id=balance.user_id;
mysql> select * from temp_user_balance; +-----------+---------+ | user_name | balance | +-----------+---------+ | 张三 | 200.00 | | 李四 | 150.00 | | 王五 | 100.00 | +-----------+---------+ 3 rows in set (0.00 sec)
mysql> select * from temp_user_balance; ERROR 1146 (42S02): Table 'test.temp_user_balance' doesn't exist mysql>
Delete temporary table
DROP TEMPORARY TABLE table_name;
Partition type
RANGE partition
It is based on a continuous interval range, Distributing data to different partitions is the most commonly used type of partition. Let's create a partition table with an id column interval.create table user(id int(11),user_name varchar(255)) partition by range(id)( partition user0 values less than (100), partition user1 values less than (200));
show global variables like "%datadir%" +---------------+-----------------+ | Variable_name | Value | +---------------+-----------------+ | datadir | /var/lib/mysql/ | +---------------+-----------------+ 1 row in set (0.00 sec)
root@hxl-PC:/var/lib/mysql/test# ls user#p#user0.ibd user#p#user1.ibd root@hxl-PC:/var/lib/mysql/test#
mysql> insert user values(50,"张三"); Query OK, 1 row affected (0.01 sec) mysql> insert user values(150,"张三"); Query OK, 1 row affected (0.01 sec) mysql> insert user values(250,"张三"); ERROR 1526 (HY000): Table has no partition for value 250 mysql>
alter table user add partition (partition user3 values less than maxvalue); mysql> insert user values(250,"张三"); Query OK, 1 row affected (0.02 sec)
select * from information_schema.partitions where table_schema=database() and table_name='user'\G;
.....
*************************** 1. row ***************************
PARTITION_METHOD: RANGE
SUBPARTITION_METHOD: NULL
PARTITION_EXPRESSION: `id`
SUBPARTITION_EXPRESSION: NULL
PARTITION_DESCRIPTION: 100
TABLE_ROWS: 1
.....LIST partition
LIST partition is similar to RANGE, except that the values of the partition column can only store specific values, which is a collection of values in an enumeration list. RANGE is a collection of continuous interval valuescreate table user (id int(11)) partition by list(id)( partition user0 values in(1,3,5,7,9), partition user1 values in(0,2,4,6,8) );
mysql> insert user values(1); Query OK, 1 row affected (0.02 sec) mysql> insert user values(2); Query OK, 1 row affected (0.01 sec) mysql> insert user values(6); Query OK, 1 row affected (0.02 sec) mysql> insert user values(9); Query OK, 1 row affected (0.01 sec) mysql> insert user values(10); ERROR 1526 (HY000): Table has no partition for value 10 mysql>
HASH partition
The purpose of HASH is to evenly distribute data into each defined partition to ensure that the amount of data in each partition is roughly the same. HASH partition There is no need to specify which partition a certain value should be saved in like RANGE and LIST. HASH partitioning is done automatically. We only need to specify the number of partitions.create table user (id int(11)) partition by hash(id) partitions 4;
mysql> select mod(500,4)
-> ;
+------------+
| mod(500,4) |
+------------+
| 0 |
+------------+information_schema.partitions, Then TABLE_ROWS of partitions 1 and 4 are both 1.
通过条件查找数据时，使用到的分区也不一样，比如查找相等的数，那么首先计算这个值应该在哪个分区，然后在进行查找，如果使用<、>来范围查找，则会使用所有分区。
还有HASH可以使用一些函数或其他有效表达式，比如创建时可以使用partition by hash(abs(id))，但并不是所有函数都可以使用，可使用的函数可以参考官网 ；
KEY分区
Key分区和HASH类似，不同的是， HASH 分区允许使用用户自定义的表达式，KEY 分区不允许使用用户自定义的表达式，需要使用 HASH 函数
KEY分区允许多列，而HASH分区只允许一列，另外在有主键或者唯一键的情况下，key中分区列可不指定，默认为主键或者唯一键，如果没有，则必须显性指定列。
create table user(id int(11)) partition by key(id) partitions 4;
但是我并没有找到关于详细分区介绍的算法，而是看到一些说通过PASSWORD的运算，没有搞懂。
Columns分区
Columns分区是5.5引入的分区类型，在此之前，RANGE分区和LIST分区只能支持整数分区，从而需要额外的函数来计算，Columns分区解决了这个问题。
Columns分区可以细分为RANGE Columns 和LIST Columns分区，支持的类型如下：
TINYINT、 SMALLINT、 MEDIUMINT、 INT ( INTEGER) 和 BIGINT，但是不支持DECIMAL或 FLOAT。
DATE和 DATETIME。
CHAR， VARCHAR， BINARY，和 VARBINARY，TEXT和 BLOB列不支持。
create table user (
a int,
b int
)
partition by range columns(a, b) (
partition p0 values less than (5, 12),
partition p1 values less than (maxvalue, maxvalue)
);现在插入一些数据
insert into user (a,b) values (4,11); insert into user (a,b) values (6,13);
第一条由于(4,11) < (5,12) 所以在p0分区，而(6,13) < (5,12) ，超出预期，在p1分区。
子分区
子分区也称为复合分区，可以对分区表RANGE和LIST上分区再进分区。
create table user (id int, purchased date)
partition by range( year(purchased) )
subpartition by hash( to_days(purchased) )
subpartitions 2 (
partition p0 values less than (1990),
partition p1 values less than (2000),
partition p2 values less than maxvalue
);MySQL可以在分区键上使用NULL，会把他当做最小分区来处理，也就是会存放到第一个分区，但是在List分区中，NULL值必须定义在列表中，否则不能被插入。
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