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假设我在客户端和地址之间有一对多的关系。SQL首选的一对多关系
客户端可以有不同地址类型(例如,家庭,邮政,工作,公司,未来)的多个地址,并且可能没有相同类型的地址或多个地址(在这种情况下,我很乐意采取第一次出现)。
我的数据由clientid,address和addresstypeid组成。 addresstypeid的首选顺序是2,3,4,1:因此,如果客户端的addresstypeid为2,则返回该记录,如果不是3则返回记录,如果不是4,则返回1,否则返回null。
是否有比这样的更优雅的方式来做到这一点?
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