在给定条件下删除表格的重复部分

Question

这是我的

message

桌子。现在我正在尝试编写一个查询，按

collection_id

（仅第一个实例）对记录进行分组 if

type

multi-store

else by

message

.

id

.

                  id                  |            collection_id             |      type      | affiliation_id |    status    | scheduled_for_date 
--------------------------------------+--------------------------------------+----------------+----------------+--------------+--------------------
 1143c066-01ed-4eb5-a146-68487de702a9 | bce85e31-4d2f-43b1-b263-57fca356856f | multi-store    | 12091          | draft        | 
 e1183732-e91d-42eb-9998-110e039cfc25 | bce85e31-4d2f-43b1-b263-57fca356856f | multi-store    | 12092          | draft        | 
 8f962a49-7da1-46d0-87b9-595788767dfe | bce85e31-4d2f-43b1-b263-57fca356856f | multi-store    | 12097          | draft        | 
 6e4dee09-7a4e-47be-bdd8-935a67bb2063 | 740f6b42-bbf1-4aeb-8fe9-6874635d9e29 | multi-store    | 12091          | draft        | 
 79afab0e-14e7-4d1b-9a15-358763743c3e | 740f6b42-bbf1-4aeb-8fe9-6874635d9e29 | multi-store    | 12092          | draft        | 
 7bc78bee-074a-4031-9492-954e7c4eeb09 | 740f6b42-bbf1-4aeb-8fe9-6874635d9e29 | multi-store    | 12097          | draft        | 
 3bb38fbd-d411-4f78-9c42-c858bf57b784 |                                      | standard-store | 10511          | draft        | 
 fbb3b175-1a3b-4515-b0b3-0ce6d6d0145f |                                      | standard-store | 10511          | draft        | 
 84004999-d2cf-4af4-bfaa-c1077d1d8621 |                                      | standard-store | 10511          | sent         | 2017-05-21
 cbea0789-6886-431a-a8e1-723d5aafc7b9 |                                      | standard-store | 10511          | scheduled    | 2019-02-12
 ec8988ff-5136-4b81-b448-cd456dc487a4 |                                      | standard-store | 10511          | review       | 2019-01-13
 0e119440-5fbc-4afe-a784-a6bcfe3a6e4d |                                      | standard-store | 10511          | draft        | 
 98503a20-4396-4809-b3ec-8e330c15afa9 |                                      | standard-store | 10511          | needs_action | 2018-12-11
 d33a9173-dc64-464f-8e58-49b4c9c2fdae |                                      | standard-store | 10511          | draft        | 
 bee0dc72-acca-44e2-82ea-d18e830f91a2 |                                      | standard-store | 10511          | sent         | 2016-03-12

所以输出会是这样的

                  id                  |            collection_id             |      type      | affiliation_id |    status    | scheduled_for_date 
--------------------------------------+--------------------------------------+----------------+----------------+--------------+--------------------
 1143c066-01ed-4eb5-a146-68487de702a9 | bce85e31-4d2f-43b1-b263-57fca356856f | multi-store    | 12091          | draft        | 
 6e4dee09-7a4e-47be-bdd8-935a67bb2063 | 740f6b42-bbf1-4aeb-8fe9-6874635d9e29 | multi-store    | 12091          | draft        | 
 3bb38fbd-d411-4f78-9c42-c858bf57b784 |                                      | standard-store | 10511          | draft        | 
 fbb3b175-1a3b-4515-b0b3-0ce6d6d0145f |                                      | standard-store | 10511          | draft        | 
 84004999-d2cf-4af4-bfaa-c1077d1d8621 |                                      | standard-store | 10511          | sent         | 2017-05-21
 cbea0789-6886-431a-a8e1-723d5aafc7b9 |                                      | standard-store | 10511          | scheduled    | 2019-02-12
 ec8988ff-5136-4b81-b448-cd456dc487a4 |                                      | standard-store | 10511          | review       | 2019-01-13
 0e119440-5fbc-4afe-a784-a6bcfe3a6e4d |                                      | standard-store | 10511          | draft        | 
 98503a20-4396-4809-b3ec-8e330c15afa9 |                                      | standard-store | 10511          | needs_action | 2018-12-11
 d33a9173-dc64-464f-8e58-49b4c9c2fdae |                                      | standard-store | 10511          | draft        | 
 bee0dc72-acca-44e2-82ea-d18e830f91a2 |                                      | standard-store | 10511          | sent         | 2016-03-12

一种方法是通过

union

：

SELECT DISTINCT ON (collection_id)
    collection_id,
    id,
    type,
    affiliation_id,
    status,
    scheduled_for_date
from
    message
where
    type = 'multi-store'

union

SELECT
    collection_id,
    id,
    type,
    affiliation_id,
    status,
    scheduled_for_date
from
    message
where
    type = 'standard-store'

但我觉得这样效率较低，另一种选择可能是基于案例的分组。但这包括需要将所有选择字段添加到组时的复杂性。

编写查询最有效的方法是什么？

Answer 1

您可以将

distinct on

子句与

case

表达式一起使用。

select distinct on (case when type='multi-store' then collection_id else id end)
  id, collection_id, type,
  affiliation_id, status, scheduled_for_date 
from the_table;

DB-Fiddle 演示