Mysql 分区介绍 —— RANGE COLUMNS分区

Posted 2020-10-27

RANGE COLUMNS和RANGE分区是非常类似的, 但是这两个也有很多不同的地方。

• 1. RANGE COLUMNS 不可以使用表达式, 只能使用列名
• 2. RANGE COLUMNS 接受一个或多个字段的列表
• 3. RANGE COLUMNS 分区列是不限制于数字列的;字符串, DATE和DATETIME 列也可以使用在分区列

基本定义:

CREATE TABLE table_name
PARTITIONED BY RANGE COLUMNS(column_list) (
    PARTITION partition_name VALUES LESS THAN (value_list)[,
    PARTITION partition_name VALUES LESS THAN (value_list)][,
    ...]
)
column_list:
    column_name[, column_name][, ...]
value_list:
    value[, value][, ...]

column_list是一个或多个列名, value_list是和column_list相对应的一个或多个值

mysql> CREATE TABLE rcx (
    ->     a INT,
    ->     b INT,
    ->     c CHAR(3),
    ->     d INT
    -> )
    -> PARTITION BY RANGE COLUMNS(a,d,c) (
    ->     PARTITION p0 VALUES LESS THAN (5,10,‘ggg‘),
    ->     PARTITION p1 VALUES LESS THAN (10,20,‘mmm‘),
    ->     PARTITION p2 VALUES LESS THAN (15,30,‘sss‘),
    ->     PARTITION p3 VALUES LESS THAN (MAXVALUE,MAXVALUE,MAXVALUE)
    -> );
Query OK, 0 rows affected (0.15 sec)

如果我们写入三条数据到这个表每个列的值是5, 三条数据都将存储在p1分区, 因为每个列的值都不小于5, 所以我们可以查询INFORMATION_SCHEMA.PARTITIONS:

mysql> INSERT INTO r1 VALUES (5,10), (5,11), (5,12);
Query OK, 3 rows affected (0.00 sec)
Records: 3  Duplicates: 0  Warnings: 0
mysql> SELECT PARTITION_NAME,TABLE_ROWS
    ->     FROM INFORMATION_SCHEMA.PARTITIONS
    ->     WHERE TABLE_NAME = ‘r1‘;
+----------------+------------+
| PARTITION_NAME | TABLE_ROWS |
+----------------+------------+
| p0             |          0 |
| p1             |          3 |
+----------------+------------+
2 rows in set (0.00 sec)

同样的, RANGE COLUMNS和RANGE分区一样, 也是支持MAXVALUE的。

CREATE TABLE rc1 (
    a INT,
    b INT
)
PARTITION BY RANGE COLUMNS(a, b) (
    PARTITION p0 VALUES LESS THAN (5, 12),
    PARTITION p3 VALUES LESS THAN (MAXVALUE, MAXVALUE)
);

但是在此时, 写入的数据分布也会发生很大变化

mysql> INSERT INTO rc1 VALUES (5,10), (5,11), (5,12);
Query OK, 3 rows affected (0.00 sec)
Records: 3  Duplicates: 0  Warnings: 0
mysql> SELECT PARTITION_NAME,TABLE_ROWS
    ->     FROM INFORMATION_SCHEMA.PARTITIONS
    ->     WHERE TABLE_NAME = ‘rc1‘;
+--------------+----------------+------------+
| TABLE_SCHEMA | PARTITION_NAME | TABLE_ROWS |
+--------------+----------------+------------+
| p            | p0             |          2 |
| p            | p1             |          1 |
+--------------+----------------+------------+
2 rows in set (0.00 sec)

因为我们比较的是行数据而非标量值

mysql> SELECT (5,10) < (5,12), (5,11) < (5,12), (5,12) < (5,12);
+-----------------+-----------------+-----------------+
| (5,10) < (5,12) | (5,11) < (5,12) | (5,12) < (5,12) |
+-----------------+-----------------+-----------------+
|               1 |               1 |               0 |
+-----------------+-----------------+-----------------+
1 row in set (0.00 sec)

如果是单个字段的RANGE COLUMNS分区, 那么和RANGE分区是一致的

CREATE TABLE rx (
    a INT,
    b INT
)
PARTITION BY RANGE COLUMNS (a)  (
    PARTITION p0 VALUES LESS THAN (5),
    PARTITION p1 VALUES LESS THAN (MAXVALUE)
);

如果我们新增行(5,10), (5, 11)和(5,12)到表中, 我们可以看到他们存储的位置是一样的

mysql> INSERT INTO rx VALUES (5,10), (5,11), (5,12);
Query OK, 3 rows affected (0.00 sec)
Records: 3  Duplicates: 0  Warnings: 0
mysql> SELECT PARTITION_NAME,TABLE_ROWS
    ->     FROM INFORMATION_SCHEMA.PARTITIONS
    ->     WHERE TABLE_NAME = ‘rx‘;
+--------------+----------------+------------+
| TABLE_SCHEMA | PARTITION_NAME | TABLE_ROWS |
+--------------+----------------+------------+
| p            | p0             |          0 |
| p            | p1             |          3 |
+--------------+----------------+------------+
2 rows in set (0.00 sec)