Parametrize the WHERE clause? - sql

Question

I'm need to write a stored procedure for SQL Server 2008 for performing a large select query and I need it to filter results with specifying filtering type via procedure's parameters. I found some solutions like this:
create table Foo(
id bigint, code char, name nvarchar(max))
go
insert into Foo values
(1,'a','aaa'),
(2,'b','bbb'),
(3,'c','ccc')
go
create procedure Bar
#FilterType nvarchar(max),
#FilterValue nvarchar(max) as
begin
select * from Foo as f
where case #FilterType
when 'by_id' then f.id
when 'by_code' then f.code
when 'by_name' then f.name end
=
case #FilterType
when 'by_id' then cast(#FilterValue as bigint)
when 'by_code' then cast(#FilterValue as char)
when 'by_name' then #FilterValue end
end
go
exec Bar 'by_id', '1';
exec Bar 'by_code', 'b';
exec Bar 'by_name', 'ccc';
I'm finding that this approach doesn't work. It's possible to cast all the columns to nvarchar(max) and compare them as strings, but I think it will cause performance degradation.
Is it possible to parametrize the where clause in stored procedure without using constructs like EXEC sp_executesql?

Answer 1

This may become a little more long winded, for large filter requirements, but I think it probably more performant/easier to read/maintain:
create procedure Bar
#Id int,
#Code nvarchar,
#name nvarchar
begin
select * from Foo as f
where (#id = -1 or f.ID = #id)
and (#Code = '' or f.Code = #Code)
and (#Name = '' or f.Name = #Name)
end
go
exec Bar 1, '', ''
exec Bar -1, 'code', ''
exec Bar -1, '', 'name'
This also allows you to filter by more than one item at the same time.

Answer 2

Try this
create procedure Bar
#FilterType nvarchar(max),
#FilterValue nvarchar(max) as
begin
select * from Foo as f
where
(#FilterType ='by_id' and f.id =cast(#FilterValue as bigint) )
OR
(#FilterType ='by_code' and f.code =cast(#FilterValue as char)
OR
(#FilterType ='by_name' and f.name =#FilterValue
end
go

Answer 3

declare #field varchar(20)
declare #value varchar(100)
set #field = 'customerid'
set #value = 'ALFKI'
set #field = 'Country'
set #value = 'Germany'
set #field = 'ContactTitle'
set #value = 'Owner'
select * from customers
where (customerid = (case when #field = 'customerid' then #value else customerid end)
and ContactTitle = (case when #field = 'ContactTitle' then #value else ContactTitle end)
and country = (case when #field = 'Country' then #value else country end))
Example is adapted for Northwind database.
Hope this helps.
EDIT: Comment any 2 out of the 3 values for #field and #value for above.

Answer 4

If you don't have many filtering criteria, you could consider creating delegate functions and dispatching the request to the appropriate one. E.g.,
create procedure Bar
#FilterType nvarchar(max),
#FilterValue nvarchar(max) as
begin
case #FilterType
when 'by_id' then FilterById(#FilterValue)
when 'by_code' then FilterByCode(#FilterValue)
when 'by_name' then FilterByName(#FilterValue)
end
end
go