My table contains the following fields, Name,Age,Salary,Phone,DOB. Based on a settings table, I have to select only some fields. For example, I say in settings, only Name and Phone is required. How can I do it using stored procedure ?
EDIT :
Which one is good.
.Visibility property to hide or show columns SQL is a fixed column language: columns can not be added or removed "on the fly"
You would need to use dynamic SQL to build a SELECT statement, or use IF statements to execute different ones. However, you open up caching, security and injection issues.
Personally, I'd ignore columns in the client code and have a simple, single efficient SQL query. The contract or API between SQL Server and the client should be static and predictable. If the settings table is applied in SQL Server, your client doesn't know what columns to expect. If your client does know, then it can ignore them.
After your edit, option 2, kind of.
But the data should be removed before being rendered in the page.
Keep it simple: don't try to optimise anything yet
You would need to have multiple different selects - based on your settings table - in your stored proc to return the different sets of data.
CREATE PROCEDURE dbo.YourProcedure(...)
AS BEGIN
DECLARE @Setting INT -- ?? whatever it is
SELECT @Setting = Choice FROM dbo.YourSettingsTable WHERE ....... ???
IF @Setting = 1
SELECT Name, Phone
FROM dbo.YourDataTable
ELSE
SELECT Name, Age, DOB, Phone, Salary
FROM dbo.YourDataTable
END
Using this approach, however, has its dangers - since the stored proc might return one set of data or quite another, your SQL Server query optimizer might make a very good decision on how to access the data for one setting - but when your setting changes, that execution plan will be totally outdated, thus potentially leading to horrible performance......
On the other hand - it might be easier to determine that setting before calling your stored proc - and then just pass in that setting as a stored proc parameter.
Or even better yet: have separate stored procs for each "scenario" - and then from the caller, call the appropriate stored proc depending on the value of your setting....
Create the sql you want dynamically then execute it with exec.
declare @sql varchar(500)
set @sql = 'select 123'
exec (@sql)
The above code should help you understand what you need to know.
