Questions About Sorting

Question

Suppose I have this table in an SQL Server database:

CREATE TABLE Widgets
	(
	WidgetID INT,
	....
	)

and I use this stored procedurre to retrieve the data:

SELECT
		WidgetID
		....
	FROM
		Widgets
	ORDER BY
		WidgetID

In my application I get the data:

Private Sub PopulateWidgets
	Dim Widgets as New List(Of Widget)
	Dim w as Widget
	....
	While rdr.Read
		w = New Widget with
			{
			.WidgetID = rdr.GetInt32(0),
			....
			}
		Widgets.Add(w)
	End While
End Sub

First question: Is Widgets guaranteed to be in sorted order?

Later, I do this:

SomeWidgets = Widgets.While(Function(wdgt) wdgt.Color = Blue)

Second question: Is SomeWidgets still guaranteed to be in sorted order on WidgetID?

Answer 1

Hi @RogerSchlueter-7899,

1. Yes, the SQL query you used to retrieve the data includes an ORDER BY WidgetID clause. This means that the data read by the SqlDataReader (rdr) will be sorted by WidgetID, and as you populate the Widgets list in the order read from the reader, the list will remain sorted by WidgetID.
2. Using the Where method (not While as in your example) to filter Widgets will maintain the order of the original list.

Dim SomeWidgets = Widgets.Where(Function(wdgt) wdgt.Color = Blue).ToList()

Best Regards.

Jiachen Li

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Answer 2

If you define a ORDER BY in your query, then it is guaranteed that you get the result in that order sorted.