PostgreSQL 11 新特性之分区表外键

对于 Postgresql 10 中的分区表，无法创建引用其他表的外键约束。

-- Postgresql 10
CREATE TABLE cities (
    city_id      int not null PRIMARY KEY,
    name         text not null
);

CREATE TABLE measurement (
    city_id         int not null REFERENCES cities(city_id),
    logdate         date not null,
    peaktemp        int,
    unitsales       int
) PARTITION BY RANGE (logdate);
ERROR:  foreign key constraints are not supported on partitioned tables
LINE 2:     city_id         int not null REFERENCES cities(city_id),
                                         ^

Postgresql 11 解决了这个限制，可以创建分区表上的外键。

-- Postgresql 11
CREATE TABLE cities (
    city_id      int not null PRIMARY KEY,
    unitsales       int
) PARTITION BY RANGE (logdate);

\d measurement
              Table "public.measurement"
  Column   |  Type   | Collation | Nullable | Default 
-----------+---------+-----------+----------+---------
 city_id   | integer |           | not null | 
 logdate   | date    |           | not null | 
 peaktemp  | integer |           |          | 
 unitsales | integer |           |          | 
Partition key: RANGE (logdate)
Foreign-key constraints:
    "measurement_city_id_fkey" FOREIGN KEY (city_id) REFERENCES cities(city_id)
Number of partitions: 0

目前，还不支持引用分区表的外键，也就是说分区表不能作为外键引用中的父表。

CREATE TABLE orders (
    order_id     int not null,
    order_date   date not null,
	PRIMARY KEY (order_id, order_date)
) PARTITION BY RANGE (order_date);

CREATE TABLE orders_detail (
    order_id     int not null,
order_item   varchar(50) not null,
FOREIGN KEY (order_id, order_date) REFERENCES orders(order_id, order_date)
) PARTITION BY RANGE (order_date);
ERROR:  cannot reference partitioned table "orders"

通常来说，分区表都是数据量很大的表，不建议创建引用分区表的外键。如果有必要，可以创建引用分区的外键。

官方文档：Table Partitioning

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