我有一个场景，你有两个表，如下所示，在两个表中，person_id或organisation_id被填充
TABLE_1
email_id, person_id, organisation_id, email_address Usage
1 NULL 12 O12@EMAIL.COM WorkEmail
2 12 NULL P12@EMAIL.COM WorkEmail
3 13 NULL P13@EMAIL.COM WorkEmail
4 14 NULL P14@EMAIL.COM WorkEmail
5 NULL 13 O13@EMAIL.COM WorkEmail
6 14 NULL P14_p@EMAIL.COM PersonalEmail
7 NULL 14 O14@EMAIL.COM PersonalEmail
8 13 NULL P13_2@EMAIL.COM WorkEmail
表_2。
registration_id, person_id, organisation_id, name, registration_Date
1 NULL 12 ORG12 10/05/2013
2 12 NULL P12 10/05/2013
3 13 NULL P13 10/05/2013
4 14 NULL P14 10/05/2013
5 NULL 13 O13 10/05/2013
6 NULL 14 O14 10/05/2013
我需要一个选择的声明，它会给我每个注册记录的workemail;注册记录有多个工作电子邮件地址 然后应该选择第一条记录（例如表1中带有email_id 3和8的记录）：
registration_id, person_id, organisation_id, name, email address
1 NULL 12 ORG12 O12@EMAIL.COM
2 12 NULL P12 P12@EMAIL.COM
3 13 NULL P13 P13@EMAIL.COM
4 14 NULL P14 P14@EMAIL.COM
5 NULL 13 O13 O13@EMAIL.COM
6 NULL 14 O14 NULL
我尝试过以下但不太确定这是否是最有效的方式;此外，它并不能完全满足我的需要：
SELECT t1.registration_id, t1.person_id, t1.organisation_id, t1.name, t2.email_Address
FROM table2 t1
LEFT JOIN table1 ON t2.person_id = t1.person_id
OR
t2.organisation_id = t1.organisation_id
答案 0 :(得分：1)
修订答案
/* setup */
create table Table_1
(
email_id bigint not null --identity(1,1)
, person_id bigint
, organisation_id bigint
, email_address nvarchar(256) not null
, Usage nvarchar(16) not null
)
insert Table_1 (email_id, person_id, organisation_id, email_address, Usage)
select 1 ,NULL ,12 ,'O12@EMAIL.COM' ,'WorkEmail'
union select 2 ,12 ,NULL ,'P12@EMAIL.COM' ,'WorkEmail'
union select 3 ,13 ,NULL ,'P13@EMAIL.COM' ,'WorkEmail'
union select 4 ,14 ,NULL ,'P14@EMAIL.COM' ,'WorkEmail'
union select 5 ,NULL ,13 ,'O13@EMAIL.COM' ,'WorkEmail'
union select 6 ,14 ,NULL ,'P14_p@EMAIL.COM' ,'PersonalEmail'
union select 7 ,NULL ,14 ,'O14@EMAIL.COM' ,'PersonalEmail'
union select 8 ,13 ,NULL ,'P13_2@EMAIL.COM' ,'WorkEmail'
create table Table_2
(
registration_id bigint not null --identity(1,1)
, person_id bigint
, organisation_id bigint
, name nvarchar(32) not null
, registration_Date date not null
)
insert Table_2 (registration_id, person_id, organisation_id, name, registration_Date)
select 1 ,NULL ,12 ,'ORG12' ,'10/05/2013'
union select 2 ,12 ,NULL ,'P12' ,'10/05/2013'
union select 3 ,13 ,NULL ,'P13' ,'10/05/2013'
union select 4 ,14 ,NULL ,'P14' ,'10/05/2013'
union select 5 ,NULL ,13 ,'O13' ,'10/05/2013'
union select 6 ,NULL ,14 ,'O14' ,'10/05/2013'
/* get the results */
SELECT t2.registration_id, t2.person_id, t2.organisation_id, t2.name, t1.email_Address
FROM table_2 t2
left outer join
(
select person_id, organisation_id, email_address
from Table_1 a
inner join
(
select MIN(email_id) email_id
from Table_1
where Usage = 'WorkEmail'
group by person_id, organisation_id
) b
on a.email_id = b.email_id
) t1
ON t2.person_id = t1.person_id
OR t2.organisation_id = t1.organisation_id
原始答案
我认为这就是你所追求的：
select x.registration_id, x.person_id, x.organisation_id, x.name, x.email_Address
from
(
SELECT t2.registration_id, t2.person_id, t2.organisation_id, t2.name, t1.email_Address, t1.usage
, row_number() over (partition by t2.registration_id, t1.usage order by t1.email_id) r
FROM table_2 t2
LEFT JOIN table_1 t1
ON t2.person_id = t1.person_id
OR t2.organisation_id = t1.organisation_id
) x
where (x.r = 1 and x.usage = 'WorkEmail') --limit to the first email address if there are multiple work email matches for the same registration (table2) record
or x.usage <> 'WorkEmail' --if it's not work email, don't limit the number
答案 1 :(得分：0)
PS。添加第二个答案以涵盖另一个点。您不想在任何地方使用Organisation_ID和Person_ID来保存两者的详细信息，而是创建一个名为Party的表，该表为每个组织和个人提供唯一的ID - 然后将其与组织/个人记录相关联。现在，您只需将一列用于您希望能够拥有个人ID和组织ID的任何表。
这是来自OO（面向对象）世界的一种常见模式，称为派对模式或派对模式（谷歌那些术语可以找到更多）。
看一下/播放下面的示例代码，以便更好地了解其工作方式/任何问题，请给我一个大喊：
/* setup */
if OBJECT_ID('Registrations') is not null drop table Registrations
if OBJECT_ID('PartyContact') is not null drop table PartyContact
if OBJECT_ID('ContactType') is not null drop table ContactType
if OBJECT_ID('Organisation') is not null drop table Organisation
if OBJECT_ID('Person') is not null drop table Person
if OBJECT_ID('Party') is not null drop table Party
go
create table ContactType
(
contactType_id int not null identity(1,1) constraint PK_ContactType primary key clustered
, name nvarchar(16) not null constraint UK_ContactType_Name unique
)
go
set identity_insert ContactType on
insert ContactType (contactType_id, name)
select 1, 'WorkEmail'
union select 2, 'PersonalEmail'
union select 3, 'Mobile/Cell'
set identity_insert ContactType off
go
create table Party
(
party_id bigint not null identity(1,1) constraint PK_Party primary key clustered
, name nvarchar(256) not null --this is duplicating the name on the Person/Organisation tables; normally this denormalisation would be bad practice, but here it assists in making data available in the table from which it will be referenced
--any other attributes which you want to be common to all parties
)
go
set identity_insert Party on
insert Party (party_id, name)
select 12, 'Rob Ottow'
union select 13, 'Ann Droid'
union select 14, 'Si Bermann'
union select 112, 'Global Mega Org'
union select 113, 'GeoTech Solutions'
union select 114, 'Think Ink inc.'
set identity_insert Party off
go
create table Person
(
person_id bigint not null identity(1,1) constraint PK_Person primary key clustered
, name nvarchar(256) not null
, party_id bigint not null constraint FK_Person_PartyId references Party(party_id)
constraint UK_Person_PartyId unique
, dob date
)
go
set identity_insert Person on
insert Person (person_id, name, party_id, dob)
select 2, 'Rob Ottow' , 12, '1984-12-25'
union select 3, 'Ann Droid' , 13, null --it's impolite to give a woman's age
union select 4, 'Si Bermann', 14, '1973-06-12'
set identity_insert Person off
go
create table Organisation --en-gb spelling since that's where I'm from
(
organisation_id bigint not null identity(1,1) constraint PK_Organisation primary key clustered
, name nvarchar(256) not null
, party_id bigint not null constraint FK_Organisation_PartyId references Party(party_id)
, taxNumber nchar(12) not null
)
go
set identity_insert Organisation on
insert Organisation (organisation_id, name, party_id, taxNumber)
select 1, 'Global Mega Org' , 112, '123456789012'
union select 2, 'GeoTech Solutions' , 113, '012345678901'
union select 3, 'Think Ink inc.' , 114, '901234567890'
set identity_insert Organisation off
go
create table PartyContact
(
partyContact_id bigint not null identity(1,1) constraint PK_PartyContract primary key clustered
, party_id bigint not null constraint FK_PartyContract_PartyId foreign key references Party(party_id)
, contactDetails nvarchar(256) not null
, contactType_id int not null constraint FK_PartyContract_ContactTypeId foreign key references ContactType(contactType_id)
)
go
set identity_insert PartyContact on
insert PartyContact (partyContact_id, party_id, contactDetails, contactType_id)
select 1 ,112 ,'O12@EMAIL.COM' ,1
union select 2 ,12 ,'P12@EMAIL.COM' ,1
union select 3 ,13 ,'P13@EMAIL.COM' ,1
union select 4 ,14 ,'P14@EMAIL.COM' ,1
union select 5 ,113 ,'O13@EMAIL.COM' ,1
union select 6 ,14 ,'P14_p@EMAIL.COM' ,2
union select 7 ,114 ,'O14@EMAIL.COM' ,2
union select 8 ,13 ,'P13_2@EMAIL.COM' ,1
union select 9 ,13 ,'01234 567890' ,3
set identity_insert PartyContact off
go
create table Registrations
(
registration_id bigint not null identity(1,1) constraint PK_Registrations primary key clustered
, party_id bigint not null constraint FK_Registrations_PartyId references Party(party_id)
, name nvarchar(32) not null
, registration_Date date not null
)
go
set identity_insert Registrations on
insert Registrations (registration_id, party_id, name, registration_Date)
select 1 ,112 ,'ORG12' ,'10/05/2013'
union select 2 ,12 ,'P12' ,'10/05/2013'
union select 3 ,13 ,'P13' ,'10/05/2013'
union select 4 ,14 ,'P14' ,'10/05/2013'
union select 5 ,113 ,'O13' ,'10/05/2013'
union select 6 ,114 ,'O14' ,'10/05/2013'
set identity_insert Registrations off
go
/* get the results */
SELECT r.registration_id, r.party_id, p.person_id, o.organisation_id, r.name, c.contactDetails
FROM Registrations r
left outer join Person p on p.party_id = r.party_id
left outer join Organisation o on o.party_id = r.party_id
left outer join
(
select party_id, contactDetails
from PartyContact a
inner join
(
select MIN(partyContact_id) partyContact_id
from PartyContact
where contactType_id in (select contactType_id from ContactType where name = 'WorkEmail')
group by party_id
) b
on a.partyContact_id = b.partyContact_id
) c
ON r.party_id = c.party_id