【PostgreSQL】分区表

--创建销售明细表，作为“父表”
create table sales_detail (
product_id    int    not null,
price         numeric(12,2),
amount        int    not null,
sale_date     date   not null,
buyer         varchar(40),
buyer_contact text
);

--根据销售日期sale_date字段，每个季度作为一个分区，创建分区表
create table sales_detail_Y2017Q01(check (sale_date >= date ‘2017-01-01‘ and sale_date < date ‘2017-04-01‘) ) inherits (sales_detail);

create table sales_detail_Y2017Q02(check (sale_date >= date ‘2017-04-01‘ and sale_date < date ‘2017-07-01‘) ) inherits (sales_detail);

create table sales_detail_Y2017Q03(check (sale_date >= date ‘2017-07-01‘ and sale_date < date ‘2017-10-01‘) ) inherits (sales_detail);

create table sales_detail_Y2017Q04(check (sale_date >= date ‘2017-10-01‘ and sale_date < date ‘2018-01-01‘) ) inherits (sales_detail);

--在分区键sale_detail上创建索引
create index sales_detail_Y2017Q01_sale_date on sales_detail_Y2017Q01 (sale_date);

create index sales_detail_Y2017Q02_sale_date on sales_detail_Y2017Q02 (sale_date);

create index sales_detail_Y2017Q03_sale_date on sales_detail_Y2017Q03 (sale_date);

create index sales_detail_Y2017Q04_sale_date on sales_detail_Y2017Q04 (sale_date);

--创建触发器，当向sales_detail表中插入数据时，可以重定向插入到分区表中
create or replace function sales_detail_insert_trigger()
returns trigger as $$
begin
    if (new.sale_date >= date ‘2017-01-01‘ and new.sale_date < date ‘2017-04-01‘) then
    insert into sales_detail_Y2017Q01 values (new.*);
    elsif (new.sale_date >= date ‘2017-04-01‘ and new.sale_date < date ‘2017-07-01‘) then
    insert into sales_detail_Y2017Q02 values (new.*);
    elsif (new.sale_date >= date ‘2017-07-01‘ and new.sale_date < date ‘2017-10-01‘) then
    insert into sales_detail_Y2017Q03 values (new.*);
    elsif (new.sale_date >= date ‘2017-10-01‘ and new.sale_date < date ‘2018-01-01‘) then
    insert into sales_detail_Y2017Q04 values (new.*);
    else 
    raise exception ‘Date out of range.Fix the sales_detail_insert_trigger () function!‘;
  end if;
  return null;
end;
$$
language plpgsql;

create trigger insert_sales_detail_trigger 
before insert on sales_detail
for each row execute procedure sales_detail_insert_trigger ();

--设置constraint_exclusion参数为“partition”状态。此参数默认为“partition”
set constrait_exclusion ‘partition‘

--向“父表”中插入一条数据
test=# insert into sales_detail values (1,23.22,1,date‘2017-08-16‘,‘zhaosi‘,‘xiangyashan222hao‘);

--数据已经插入到分区表中
test=# select * from sales_detail_Y2017Q03;
 product_id | price | amount | sale_date  | buyer  |   buyer_contact   
------------+-------+--------+------------+--------+-------------------
          1 | 23.22 |      1 | 2017-08-16 | zhaosi | xiangyashan222hao
(1 row)

--并且查询“父表”也可以查到插入的数据
test=# select * from sales_detail;
 product_id | price | amount | sale_date  | buyer  |   buyer_contact   
------------+-------+--------+------------+--------+-------------------
          1 | 23.22 |      1 | 2017-08-16 | zhaosi | xiangyashan222hao
(1 row)

--通过查看执行计划，可以看出当查询数据时，数据库会自动的去sales_detail_Y2017Q03分区表中查找，而不会扫描所有的分区表。
test=# explain select * from sales_detail where sale_date=date‘2017-08-16‘;
                                             QUERY PLAN                                             
----------------------------------------------------------------------------------------------------
 Append  (cost=0.00..9.50 rows=3 width=158)
   ->  Seq Scan on sales_detail  (cost=0.00..0.00 rows=1 width=158)
         Filter: (sale_date = ‘2017-08-16‘::date)
   ->  Bitmap Heap Scan on sales_detail_y2017q03  (cost=4.16..9.50 rows=2 width=158)
         Recheck Cond: (sale_date = ‘2017-08-16‘::date)
         ->  Bitmap Index Scan on sales_detail_y2017q03_sale_date  (cost=0.00..4.16 rows=2 width=0)
               Index Cond: (sale_date = ‘2017-08-16‘::date)
(7 rows)