Join Query

Hi,
I have 3 tables as follows (simplified for posting here):
Table1
--
CREATE TABLE [dbo].[Customer] (
[CustomerID] [int] IDENTITY (1, 1) NOT NULL ,
[CustomerName] [varchar] (50) NOT NULL
) ON [PRIMARY]
Table2
--
CREATE TABLE [dbo].[Supplier] (
[SupplierID] [int] IDENTITY (1, 1) NOT NULL ,
[SupplierName] [varchar] (50) NOT NULL
) ON [PRIMARY]
Table3
--
CREATE TABLE [dbo].[PhoneBook] (
[PBID] [int] IDENTITY (1, 1) NOT NULL ,
[PhoneNumber] [varchar] (50) NOT NULL ,
[ContactType] [varchar] (10) NOT NULL ,
[ContactID] [int] NOT NULL
) ON [PRIMARY]
The ContactType column in Table3 (PhoneBook) has 2 possible values (Customer
and Supplier) and the ContactID column will either have CustomerID or
SupplierID stored in it based on the ContactType.
Now I am trying to write a query that will return me all records from the
3rd table (PhoneBook) along with the original names. I have come up with
this:
Query:
--
Select
P.PBID,
P.PhoneNumber ,
IsNull(C.CustomerName, '') + IsNull(S.SupplierName, '') As
ContactName,
P.Contacttype
From
PhoneBook P
Left Outer Join Customer C On P.ContactID = C.CustomerID and
P.Contacttype = 'Customer'
Left Outer Join Supplier S On P.ContactID = S.SupplierID and
P.Contacttype = 'Supplier'
Obviously I'm new to writing queries and I know that there is probably a
much better way to write this query. This query seems inelegant and
probably very poorly written. I am hoping someone can help me come up with
a better queries.
Thanks in advance!
AbhinavHow are enforcing data integrity between the Customer and Supplier
tables and the PhoneBook table? Since you can't use a foreign key, [as
it references 2 separate tables], I assume you have a trigger? The FK is
more solid, btw. [if you don't have anything in the database to do this,
consider the fact that anyone that can add data to the database can add
data to this table that does not have valid referenced values.]
You really should have 2 separate phonebook tables, since you have 2
referenced tables (and therefore are representing 2 distinct phonebook
entities), with FKs.
That said, if you can't/won't change it, you can use a UNION ALL.
Select
P.PBID,
P.PhoneNumber ,
C.CustomerName As ContactName,
P.Contacttype
From
PhoneBook P
Join Customer C On P.ContactID = C.CustomerID
where
P.Contacttype = 'Customer'
UNION ALL
select
p.pbid,
p.phonenumber,
s.suppliername as ContactName,
P.contacttype
from
phonebook p
join Supplier S On P.ContactID = S.SupplierID
where
P.Contacttype = 'Supplier'
[to get one phonebook from the 2 i recommend, you could do the same thing]
A J wrote:
> Hi,
> I have 3 tables as follows (simplified for posting here):
> Table1
> --
> CREATE TABLE [dbo].[Customer] (
> [CustomerID] [int] IDENTITY (1, 1) NOT NULL ,
> [CustomerName] [varchar] (50) NOT NULL
> ) ON [PRIMARY]
>
> Table2
> --
> CREATE TABLE [dbo].[Supplier] (
> [SupplierID] [int] IDENTITY (1, 1) NOT NULL ,
> [SupplierName] [varchar] (50) NOT NULL
> ) ON [PRIMARY]
>
> Table3
> --
> CREATE TABLE [dbo].[PhoneBook] (
> [PBID] [int] IDENTITY (1, 1) NOT NULL ,
> [PhoneNumber] [varchar] (50) NOT NULL ,
> [ContactType] [varchar] (10) NOT NULL ,
> [ContactID] [int] NOT NULL
> ) ON [PRIMARY]
>
> The ContactType column in Table3 (PhoneBook) has 2 possible values (Custom
er
> and Supplier) and the ContactID column will either have CustomerID or
> SupplierID stored in it based on the ContactType.
> Now I am trying to write a query that will return me all records from the
> 3rd table (PhoneBook) along with the original names. I have come up with
> this:
> Query:
> --
> Select
> P.PBID,
> P.PhoneNumber ,
> IsNull(C.CustomerName, '') + IsNull(S.SupplierName, '') As
> ContactName,
> P.Contacttype
> From
> PhoneBook P
> Left Outer Join Customer C On P.ContactID = C.CustomerID and
> P.Contacttype = 'Customer'
> Left Outer Join Supplier S On P.ContactID = S.SupplierID and
> P.Contacttype = 'Supplier'
> Obviously I'm new to writing queries and I know that there is probably a
> much better way to write this query. This query seems inelegant and
> probably very poorly written. I am hoping someone can help me come up wit
h
> a better queries.
> Thanks in advance!
> Abhinav
>|||Assuming you reject Trey's idea to have a schema that properly enforces
referential integrity. I don't think your sql is too bad. The only thing
that is "inelegant" is the ContactName portion. I think it should just be
something like this:
Select
P.PBID,
P.PhoneNumber ,
IsNull(C.CustomerName, S.SupplierName) As
ContactName,
P.Contacttype
From
PhoneBook P
Left Outer Join Customer C On P.ContactID = C.CustomerID and
P.Contacttype = 'Customer'
Left Outer Join Supplier S On P.ContactID = S.SupplierID and
P.Contacttype = 'Supplier'
In my opinion, this is better than the union all approach.
"A J" wrote:

> Hi,
> I have 3 tables as follows (simplified for posting here):
> Table1
> --
> CREATE TABLE [dbo].[Customer] (
> [CustomerID] [int] IDENTITY (1, 1) NOT NULL ,
> [CustomerName] [varchar] (50) NOT NULL
> ) ON [PRIMARY]
>
> Table2
> --
> CREATE TABLE [dbo].[Supplier] (
> [SupplierID] [int] IDENTITY (1, 1) NOT NULL ,
> [SupplierName] [varchar] (50) NOT NULL
> ) ON [PRIMARY]
>
> Table3
> --
> CREATE TABLE [dbo].[PhoneBook] (
> [PBID] [int] IDENTITY (1, 1) NOT NULL ,
> [PhoneNumber] [varchar] (50) NOT NULL ,
> [ContactType] [varchar] (10) NOT NULL ,
> [ContactID] [int] NOT NULL
> ) ON [PRIMARY]
>
> The ContactType column in Table3 (PhoneBook) has 2 possible values (Custom
er
> and Supplier) and the ContactID column will either have CustomerID or
> SupplierID stored in it based on the ContactType.
> Now I am trying to write a query that will return me all records from the
> 3rd table (PhoneBook) along with the original names. I have come up with
> this:
> Query:
> --
> Select
> P.PBID,
> P.PhoneNumber ,
> IsNull(C.CustomerName, '') + IsNull(S.SupplierName, '') As
> ContactName,
> P.Contacttype
> From
> PhoneBook P
> Left Outer Join Customer C On P.ContactID = C.CustomerID and
> P.Contacttype = 'Customer'
> Left Outer Join Supplier S On P.ContactID = S.SupplierID and
> P.Contacttype = 'Supplier'
> Obviously I'm new to writing queries and I know that there is probably a
> much better way to write this query. This query seems inelegant and
> probably very poorly written. I am hoping someone can help me come up wit
h
> a better queries.
> Thanks in advance!
> Abhinav
>
>