Using a parameter in UDF from clause - sql-server-2008

Question

I have a User defined function in SQL Server 2008. Here it is:
CREATE FUNCTION [dbo].[GetAddressByEntityNameAndId]
(
-- Add the parameters for the function here
#entityName varchar (100),
#parentEntityId int
)
RETURNS varchar(300)
AS
BEGIN
-- Declare the return variable here
DECLARE #Address varchar(300)
if(#entityName = 'Staff')
BEGIN
select #Address = ca.Address + ' ' + ca.City + ' ' + ca.State + ' ' + ca.ZipCode
from #entityName cc
inner join ContactAddress ca on ca.ParentEntityId = cc.Id
inner join EntityName en on en.Id = ca.EntityNameId and en.Name = #entityName
inner join GeneralLookup gl on ca.glAddressTypeId = gl.Id and gl.LookupItem = 'Primary'
where cc.Id = #parentEntityId
END
-- Return the result of the function
RETURN #Address
END
But it does not get executed. Error message is:
Must declare the table variable "#entityName".
Any help would be appreciated.
UPDATE:
Ok now I have another problem. This is my SP:
ALTER PROCEDURE [dbo].[spGetStaffsAndClients]
AS
BEGIN
declare #Address varchar (100)
declare #Apartment varchar (100)
declare #City varchar (100)
declare #State varchar (10)
declare #Zip varchar (10)
declare #County varchar (100)
-- SET NOCOUNT ON added to prevent extra result sets from
-- interfering with SELECT statements.
SET NOCOUNT ON;
-- Insert statements for procedure here
/* Get Client's Residence */
select dbo.GetClientFullName(s.FirstName, s.MiddleInit, s.LastName) StaffName,
dbo.GetStaffTitlesById(s.Id) StaffTitle,
dbo.GetClientFullName(c.FirstName, c.MiddleInit, c.LastName) ClientName,
dbo.GetAddressByEntityNameAndId('Client', c.Id) ClientAddress
from ClientStaff cs
left outer join Staff s on cs.StaffId = s.Id
left outer join Client c on cs.ClientId = c.Id
END
This is UDF:
ALTER FUNCTION [dbo].[GetAddressByEntityNameAndId]
(
-- Add the parameters for the function here
#entityName varchar (100),
#parentEntityId int
)
RETURNS varchar(300)
AS
BEGIN
-- Declare the return variable here
DECLARE #Address varchar(300)
if(#entityName = 'Client')
BEGIN
select #Address = ca.Address + ' ' + ca.City + ' ' + ca.State + ' ' + ca.ZipCode
from Client cc
inner join ContactAddress ca on ca.ParentEntityId = cc.Id
inner join EntityName en on en.Id = ca.EntityNameId and en.Name = cc.Id
inner join GeneralLookup gl on ca.glAddressTypeId = gl.Id and gl.LookupItem = 'Primary'
where cc.Id = #parentEntityId
END
-- Return the result of the function
RETURN #Address
END
I am executing the SP and getting error:
Conversion failed when converting the varchar value 'Client' to data type int.
I am unable to sort out the problem. Any help ?

Answer 1

You can't use #entityName in the from clause instead of a table name. Since you only test on Staff you can use from Staff cc instead. The only way I know of to have a variable table name in the from clause is to use dynamic SQL. And I don't think you can use dynamic SQL in functions.
Read more about dynamic queries here http://www.sommarskog.se/dynamic_sql.html.