Question

我有以下表结构：

dev=> \d membership_subscription
                                        Table "public.membership_subscription"
       Column       |           Type           |                              Modifiers                               
--------------------+--------------------------+----------------------------------------------------------------------
 id                 | integer                  | not null default nextval('membership_subscription_id_seq'::regclass)
 membership_id      | bigint                   | not null
 name               | character varying        | not null
 description        | character varying        | 
 price_gross        | integer                  | not null
 price_net          | integer                  | not null
 tax                | double precision         | not null
 priority           | integer                  | not null default 0
 currency_code      | character varying        | not null
 calculated_gross   | integer                  | not null
 calculated_net     | integer                  | not null
 state              | character varying        | 
 reference_date     | timestamp with time zone | not null
 created_at         | timestamp with time zone | not null
 created_by         | json                     | not null
 updated_at         | timestamp with time zone | not null
 updated_by         | json                     | not null
 payment_method_id  | bigint                   | 
 code               | character varying        | 
 bookings_per_month | integer                  | not null default 0
 bookings_per_venue | integer                  | not null default 0
Indexes:
    "membership_subscription_pkey" PRIMARY KEY, btree (id)
    "membership_id_reference_date_index" UNIQUE, btree (membership_id, reference_date)
Foreign-key constraints:
    "membership_subscription_membership_id_fkey" FOREIGN KEY (membership_id) REFERENCES membership(id) ON UPDATE CASCADE
    "membership_subscription_payment_method_id_fkey" FOREIGN KEY (payment_method_id) REFERENCES payment_saved_method(id) ON UPDATE CASCADE ON DELETE SET NULL

我想：

SELECT membership _id＆amp;名称
GROUP BY membership_id
获取最大reference_date
不在（＆＃39; new＆＃39;，＆＃39; discurded＆＃39;）

注意：每个会员都有12个订阅，所以我想选择那些只处于状态（＆＃39; new＆＃39;，＆＃39;丢弃＆＃39;）然后是它们的最大reference_date

我的尝试：

dev=> SELECT membership_id, name FROM membership_subscription WHERE state NOT IN ('new', 'discurded') GROUP BY membership_id, name, reference_date ORDER BY reference_date DESC;

但是没有回复对我的预期

Answer 1

WITH membership_subscription(membership_id,name,state,reference_date) AS ( VALUES
  (1,'name-1','new','2016-03-18'::DATE),
  (1,'name-2','discurded','2016-03-17'::DATE),
  (1,'name-3','state 1','2016-03-16'::DATE), -- record #1 to select 
  (1,'name-4','state 2','2016-03-15'::DATE), 
  (2,'name-5','new','2015-03-15'::DATE),
  (2,'name-6','discurded','2015-03-16'::DATE),
  (2,'name-7','state 3','2015-03-17'::DATE),
  (2,'name-8','state 4','2015-03-18'::DATE) -- record #2 to select
)
SELECT
  DISTINCT ON (membership_id)
  membership_id,
  name,
  max(reference_date)
FROM membership_subscription
WHERE state NOT IN ('new','discurded')
GROUP BY membership_id,name;

Answer 2

您的错误是将reference_date包含在分组中，将其删除，您的查询应该有效。要在每个组中获取最新的reference_date，您应该使用最大聚合函数

代码（我没有测试它）：

SELECT membership_id, name, max(reference_date) FROM membership_subscription WHERE state NOT IN ('new', 'discurded') GROUP BY membership_id, name ORDER BY 3 DESC;

PSQL：选择子查询和分组依据

2 个答案: