How to get SQL Data in chunks from remote server

OFFSET FETCH is a feature added to the ORDER BY clause beginning with the SQL Server 2012 edition. It can be used to extract a specific number of rows starting from a specific index.

Here is a simple example;

SELECT * FROM [dbo].[tblSample] 
order by SampleId 
OFFSET 0 ROWS
FETCH NEXT 10 ROWS ONLY

This instruct SQL Server to start from first record and return 10 records only.

Let’s write a dynamic sql to get data in batches; For example we have 7 records from database and we would like to get 3 records on each round trip;

DECLARE @RowCount INT, @RowIncrement INT, @RowsInChunk INT, @RemainingRows INT, @SourceQuery NVARCHAR(255)
DECLARE @RowIncrementValue INT, @BatchValue INT
DECLARE @SQL_Select NVARCHAR(4000);
DECLARE @RowIncrementCheck INT;

SET @RowCount = 7;
SET @RowIncrement = 0;
SET @RowsInChunk = 3;

--initial value
SET @RowIncrementValue = @RowIncrement
SET @BatchValue = @RowsInChunk

--loop through all records
WHILE (@RowIncrement <= @RowCount)
BEGIN

	--prepare SQL statement
	SET @SQL_Select =
	'SELECT *
	FROM [dbo].[tblSample] 
	order by SampleId 
	OFFSET  ' + CAST(@RowIncrementValue AS NVARCHAR) + ' ROWS ' + CHAR(13) +
	'FETCH NEXT ' + CAST(@BatchValue AS NVARCHAR) + ' ROWS ONLY'

	--EXECUTE sp_executesql @SQL_Select
	PRINT @SQL_SELECT

	SET @RowIncrement = @RowIncrement + @RowsInChunk
	SET @RowIncrementValue = @RowIncrement

	--calculate remaining rows
	SET @RemainingRows = @RowCount - @RowIncrement
	PRINT 'Remaining Rows ' +  CAST(@RemainingRows AS NVARCHAR)
	IF (@RemainingRows <= @RowsInChunk) AND (@RowIncrement <= @RowCount)
	BEGIN
		--short circuit this loop
		SET @BatchValue = @RemainingRows
		SET @RowIncrement = @RowCount
	END
END

Here is the result of 3 dynamic sql for 7 records;

SELECT *
	FROM [dbo].[tblSample] 
	order by SampleId 
	OFFSET  0 ROWS 
FETCH NEXT 3 ROWS ONLY
SELECT *
	FROM [dbo].[tblSample] 
	order by SampleId 
	OFFSET  3 ROWS 
FETCH NEXT 3 ROWS ONLY
SELECT *
	FROM [dbo].[tblSample] 
	order by SampleId 
	OFFSET  6 ROWS 
FETCH NEXT 1 ROWS ONLY

In the query above, OFFSET 0 is used to skip 0 rows and FETCH 3 ROWS ONLY is used to extract only 3 rows.

To get additional information about the ORDER BY clause and OFFSET FETCH feature, refer to the official documentation: Using OFFSET and FETCH to limit the rows returned.

Resources

Getting data from remote server

C# expression trees

We want to treat lambda expressions as expression trees and look inside them instead of executing them. For example, LINQ to SQL gets the expression and converts it to the equivalent SQL statement and submits it to server (rather than executing the lambda).

With Lambda expressions we can write less code, and the code will be more readable.

A lambda expression uses the lambda operator => which means goes to.

arguments => expession

The expression reads: arguments goes to expression.

Let’s start with a common example;

using System;

namespace Lambdas
{
    class Program
    {
        static void Main()
        {
            Console.WriteLine(Square(5));
            Console.ReadLine();
        }

        static int Square(int num)
        {
            return num * num;
        }
    }
}

we declare a method called Square of type int with one input parameter of type int. It multiplies the number and returns the result.

In the Main() method we call our Square method with an int as a parameter.

We can convert this function into a Lambda expression. This is what it would look like:

num => num * num;

This expression would read: num goes to calculation (num * num).

This expression is short and easily readable once we get used to it. The catch though, is that a Lambda expression must be assigned to a delegate.

Resources

https://stackoverflow.com/questions/793571/why-would-you-use-expressionfunct-rather-than-funct

https://tyrrrz.me/blog/expression-trees

https://thesharperdev.com/an-introduction-to-c-expression-trees/

Remove all spaces from strings using sql

I wanted to remove following spaces and special characters from these strings;

'a. Personnel '
'j.  Indirect Charges '

I tried to use following SQL to get rid of all spaces;

SELECT DISTINCT TRIM(LOWER(REPLACE(BudgetCategories, ' ', ''))) BudgetCategories
FROM [dbo].[MyTable]

Still the trailing spaces were there. I guess there is a special character involved, so i tried this one;

SELECT DISTINCT LTRIM(RTRIM(LOWER((REPLACE(REPLACE(REPLACE(REPLACE(REPLACE(BudgetCategories, ' ', ''), CHAR(10), CHAR(32)),CHAR(13), CHAR(32)),CHAR(160), CHAR(32)),CHAR(9),CHAR(32))))))
FROM [dbo].[MyTable]

This did the trick and I was able to get this output;

'a.personnel'
'j.indirectcharges'

References

https://stackoverflow.com/questions/21585914/trim-spaces-in-string-ltrim-rtrim-not-working

SQL Server Transaction block

This is suggested code block for creating stored procedures in SQL Server;

BEGIN TRY
	BEGIN TRANSACTION
	--All your insert/update/delete/merge goes in here
	COMMIT TRANSACTION
END TRY

BEGIN CATCH
	SELECT ERROR_NUMBER() AS ErrorNumber
	,ERROR_MESSAGE() AS ErrorMessage
	 ROLLBACK TRANSACTION
END CATCH

While manipulating multiple tables, the transaction would be roll back if there is any error.