如何从SQL Server中的表中检索前N行或所有行

Question

I have a datagridview in which a user is allowed to retriev either n records (using textbox) or All records by clicking on a buttun

Now want to retrieve Top N records Or All Records with a single Query. right now I'm using 2 different Queries to achieve.

//retrieving Top N Records
 SELECT Top @Rows FROM CaseDetails //@Row is parameter 

And

 //retrieving All records
SELECT Top (SELECT COUNT(*) FROM CaseDetails) FROM CaseDetails

How can i Use a single query in SQL Server to perform these 2 options ?

Answer 1

This is a tricky one.

Really you'd probably pass @Rows in all cases, or NULL to select all rows, then null coalesce via ISNULL to select the count from the table to get all rows.

// Set the Rows param first
SELECT @Rows = ISNULL(@Rows, (SELECT COUNT(*) FROM CaseDetails))

// @Rows is parameter
SELECT TOP @Rows * FROM CaseDetails

Answer 2

I think you better off by creating a procedure like

create procedure sp_fetch 
@row int = NULL
as
begin
if @row = 0 or @row is null
SELECT * FROM CaseDetails
else
select top @row * from CaseDetails
end

Then you can just call your procedure like

exec sp_fetch(10)

Answer 3

You don't need to count all rows before selecting. Assuming @Rows is an int, then you can use the max value of an int as your default. So, if @Rows is 0 or null, return all rows, otherwise, return @Rows rows:

SELECT TOP (ISNULL(NULLIF(@Rows,0), 2147483647)) * FROM CaseDetails;

Answer 4

This is working fine

Declare parameters

Create Procedure uspRetrieve
@Rows int =NULL
AS
BEGIN
   SET NOCOUNT ON;

   SET ROWCOUNT @Rows
   SELECT * FROM CaseDetails
End

IF you supply @Row=0 you will get all records else you get @Row =your limit