SQL首選一對多關系

Question

假設我在客戶端和地址之間有一對多的關系。

客戶端可以有多個具有不同地址類型的地址（例如，家庭，郵政，工作，公司，未來），並且可能沒有相同類型的地址或多個地址（在這種情況下，我很樂意第一次出現）。

我的數據包括clientid，address和addresstypeid。 addresstypeid的首選順序是2,3,4,1：所以如果客戶端的addresstypeid為2，則返回該值，如果不返回3，如果不是4，則返回，如果不是1，則返回null。

有沒有更優雅的方式來做這個比這樣的事情？

declare @addresses table
(
    clientid int,
    address varchar(10),
    addresstypeid int
)
--2,3,4,1
insert into @addresses (clientid, address, addresstypeid)
select 1, '1a', 1 union all
select 1, '1b', 2 union all
select 1, '1c', 3 union all
select 1, '1d', 4 union all
select 2, '2a', 2 union all
select 2, '2b', 3 union all
select 2, '2c', 4 union all
select 2, '2a', 1 union all
select 3, '3a', 3 union all
select 3, '3b', 4 union all
select 3, '3c', 1 union all
select 4, '4a', 3 union all
select 4, '4b', 4 union all
select 5, '5a', 4 union all
select 6, '6a', 4 union all
select 6, '6b', 1 union all
select 7, '7a', 1 union all
select 7, '7b', 4  

declare @ranktable table
(
    addresstypeid int,
    rank int
)

insert into @ranktable(addresstypeid, rank)
select 2, 1 union all
select 3, 2 union all
select 4, 3 union all
select 1, 4 

select
    e.address,
    e.clientid,
    e.addresstypeid
from
    @addresses e
    inner join @ranktable r on
        e.addresstypeid = r.addresstypeid
    inner join (select
                    em.clientid,
                    min(rank) minrank
                from @addresses em
                    inner join @ranktable ranks on
                        em.addresstypeid = ranks.addresstypeid
                group by
                    clientid) clientranks on
        e.clientid = clientranks.clientid and
        r.rank = clientranks.minrank

Answer 1

這兩個表很好，但是當你把它們永久化時你應該考慮索引:)

就你的最終查詢而言，我會稍微改變一下......

WITH
  sorted_data
AS
(
  SELECT
    [a].*,
    ROW_NUMBER() OVER (PARTITION BY [a].clientid ORDER BY [r].rank) AS sequence_id
  FROM
    @addresses     AS [a]
  INNER JOIN
    @ranktable     AS [r]
      ON a.addresstypeid = r.addresstypeid
)

SELECT
  *
FROM
  sorted_data
WHERE
  sequence_id = 1