如何使用连接语句

Question

我正在设计一个简单的办公室门票系统，并希望为负责下一步行动的一方提供一个字段。为了做到这一点，我正在考虑使用tableName和tableID作为特定责任方的指定人员（可以是技术人员，客户或第三方，所有人都在不同的表格中）< / p>

将数据拉入并使用表的名称作为参数运行另一个select调用是可以的，但额外的数据流会显着减慢速度。

有没有办法使用单个join语句返回聚会的详细信息，其中包含表名的列和一个用于单个表id的列，或者是否有更好的方法来存储来自多个潜在表的数据？ / p>

Answer 1

您可以使用左连接来满足您的要求： -

Set Nocount On;

Declare @OfficeTickets Table
(
     Id             Int Identity(1,1)
    ,Column1        Varchar(100)
    ,PartyType      Varchar(1)
    ,TechnicianId   Int Null
    ,CustomerId     Int Null
    ,ThirdPartyId   Int Null
)

Declare @OfficeTickets1 Table
(
     Id             Int Identity(1,1)
    ,Column1        Varchar(100)
    ,TableName      Varchar(100)
    ,TableId        Int Null
)

Declare @Technician Table
(
     Id             Int Identity(1,1)
    ,TechnicianName Varchar(100)
)

Declare @Customers Table
(
     Id             Int Identity(1,1)
    ,CustomerName   Varchar(100)
)

Declare @ThirdParty Table
(
     Id             Int Identity(1,1)
    ,ThirdPartyName Varchar(100)
)

Insert Into @Technician(TechnicianName) Values
 ('Technician_1')
,('Technician_2')
,('Technician_3')

Insert Into @Customers(CustomerName) Values
 ('Customer_1')
,('Customer_2')
,('Customer_3')

Insert Into @ThirdParty(ThirdPartyName) Values
 ('ThirdParty_1')
,('ThirdParty_2')
,('ThirdParty_3')
,('ThirdParty_4')

Insert Into @OfficeTickets(Column1,PartyType,TechnicianId,CustomerId,ThirdPartyId) Values
 ('ABC','T',3,Null,Null)
,('XYZ','C',Null,2,Null)
,('PUQ','P',Null,Null,4)

Insert Into @OfficeTickets1(Column1,TableName,TableId) Values
 ('ABC','Technician',3)
,('XYZ','Customers',2)
,('PUQ','ThirdParty',4)

---- taken separate columns for parties
Select   ot.Id
        ,ot.Column1
        ,t.TechnicianName
        ,c.CustomerName
        ,tp.ThirdPartyName
From    @OfficeTickets As ot
        Left Join @Technician As t On ot.PartyType = 'T' And ot.TechnicianId = t.Id
        Left Join @Customers As c On ot.PartyType = 'C' And ot.CustomerId = c.Id
        Left Join @ThirdParty As tp On ot.PartyType = 'P' And ot.ThirdPartyId = tp.Id

---- by TableName and TableId
Select   ot.Id
        ,ot.Column1
        ,t.TechnicianName
        ,c.CustomerName
        ,tp.ThirdPartyName
From    @OfficeTickets1 As ot
        Left Join @Technician As t On ot.TableName = 'Technician' And ot.TableId = t.Id
        Left Join @Customers As c On ot.TableName = 'Customers' And ot.TableId = c.Id
        Left Join @ThirdParty As tp On ot.TableName = 'ThirdParty' And ot.TableId = tp.Id

<强>输出： -