PostgreSQL组合分区及修改分区表分区范围

oracle中支持多种分区类型的组合，组合分区是range、hash、list分区的相互组合，但不允许hash分区作为 Top level。
pg中同样也支持类似的组合分区，PG支持非常灵活的分区布局，支持任意层级的分区，支持每个分区的层级深度不一样。通过detach、attach的方法来实现分区的拆分、合并。
下面以hash分区为例，使用拆分合并的方法实现组合分区。

–创建hash分区表
共4个分区

bill=# create table t_hash (id int , info text) PARTITION BY hash (id);  
CREATE TABLE
bill=# create table t_hash0 partition of t_hash FOR VALUES with (MODULUS 4, REMAINDER 0);  
CREATE TABLE
bill=# create table t_hash1 partition of t_hash FOR VALUES with (MODULUS 4, REMAINDER 1);  
CREATE TABLE
bill=# create table t_hash2 partition of t_hash FOR VALUES with (MODULUS 4, REMAINDER 2);  
CREATE TABLE
bill=# create table t_hash3 partition of t_hash FOR VALUES with (MODULUS 4, REMAINDER 3);  
CREATE TABLE

--查看分区表

```sql
bill=# \d+ t_hash
                             Partitioned table "public.t_hash"
 Column |  Type   | Collation | Nullable | Default | Storage  | Stats target | Description 
--------+---------+-----------+----------+---------+----------+--------------+-------------
 id     | integer |           |          |         | plain    |              | 
 info   | text    |           |          |         | extended |              | 
Partition key: HASH (id)
Partitions: t_hash0 FOR VALUES WITH (modulus 4, remainder 0),
            t_hash1 FOR VALUES WITH (modulus 4, remainder 1),
            t_hash2 FOR VALUES WITH (modulus 4, remainder 2),
            t_hash3 FOR VALUES WITH (modulus 4, remainder 3)

–插入数据

bill=# insert into t_hash select generate_series(1,10);
INSERT 0 10

–查看数据分布

bill=# select tableoid::regclass,* from t_hash;
 tableoid | id | info 
----------+----+------
 t_hash0  |  1 | 
 t_hash1  |  3 | 
 t_hash1  |  5 | 
 t_hash1  |  8 | 
 t_hash1  |  9 | 
 t_hash2  |  2 | 
 t_hash3  |  4 | 
 t_hash3  |  6 | 
 t_hash3  |  7 | 
 t_hash3  | 10 | 
(10 rows)

接下来将t_hash1分区拆分成2个分区，即其它分区作为直接分区，而t_hash1分区被1个二级分区代替。

–解绑分区

bill=# alter table t_hash DETACH PARTITION t_hash1;  
ALTER TABLE

–创建二级分区

bill=# create table t_hash1_subp (id int, info text) PARTITION BY hash (id);;
CREATE TABLE
bill=# create table t_hash1_subp1 partition of t_hash1_subp FOR VALUES with (MODULUS 8, REMAINDER 1);  
CREATE TABLE
bill=# create table t_hash1_subp5 partition of t_hash1_subp FOR VALUES with (MODULUS 8, REMAINDER 5);
CREATE TABLE

–绑定二级分区到一级分区

bill=# alter table t_hash attach partition t_hash1_subp FOR VALUES WITH ( MODULUS 4, REMAINDER 1 ); 
ALTER TABLE

–将原来子分区的数据写入新的二级分区表(数据迁移)

bill=# insert into t_hash1_subp select * from t_hash1; 
INSERT 0 4

–查询数据

bill=# select tableoid::regclass,* from t_hash;  
   tableoid    | id | info 
---------------+----+------
 t_hash0       |  1 | 
 t_hash1_subp1 |  3 | 
 t_hash1_subp5 |  5 | 
 t_hash1_subp5 |  8 | 
 t_hash1_subp5 |  9 | 
 t_hash2       |  2 | 
 t_hash3       |  4 | 
 t_hash3       |  6 | 
 t_hash3       |  7 | 
 t_hash3       | 10 | 
(10 rows)

–查看分区表情况
可以发现分区表变成了非平衡的复合分区

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bill=# \d+ t_hash
                             Partitioned table "public.t_hash"
 Column |  Type   | Collation | Nullable | Default | Storage  | Stats target | Description 
--------+---------+-----------+----------+---------+----------+--------------+-------------
 id     | integer |           |          |         | plain    |              | 
 info   | text    |           |          |         | extended |              | 
Partition key: HASH (id)
Partitions: t_hash0 FOR VALUES WITH (modulus 4, remainder 0),
            t_hash1_subp FOR VALUES WITH (modulus 4, remainder 1), PARTITIONED,
            t_hash2 FOR VALUES WITH (modulus 4, remainder 2),
            t_hash3 FOR VALUES WITH (modulus 4, remainder 3)

同样，我们还可以将其它分区拆分，例如将t_hash2拆分成range分区或者list分区，实现oracle组合分区一样的功能，且更加灵活(支持hash分区作为一级分区)。