Convert nvarchar to int in SQL

If your table has nvarchar column and there is integer data in this column , then inserting that data into int column type is not a problem.
But if data is float, then the data need to be converted to float datatype before cast to int to insert into int column type.

Example:
SELECT SUM(CAST(amount AS INT)),  title   FROM books GROUP BY title
...will give you:

Conversion failed when converting the nvarchar value '4500.00' to data type int.

Correct way

4500.00 is not integer so CAST via float first

sum(CAST(CAST(amount AS float) AS INT))

Why float?

• no idea of precision or scale across all rows
• empty string will cast to zero for float, fails on decimal
• float accepts stuff like 7E-02, fails on decimal 

HTH

STATISTICS_NORECOMPUTE in Rebuild Index

It specifies whether distribution statistics are recomputed. The default is OFF.

ON

Out-of-date statistics are not automatically recomputed.

OFF

Automatic statistics updating are enabled.

Indeed, statistics are recomputed during the index rebuild.

Dont think that it stops SQL Server from updating the statistics at the time of a rebuild; that is NOT what it does. 
Statistics are ALWAYS updated at the time of a REBUILD; this cannot be turned off (nor would you want to).

Instead, STATISTICS_NORECOMPUTE stops the database-wide auto-updating from updating the specific statistics for an index (or column-level statistic) that was created (or rebuilt) with this option turned on.

STATISTICS_NORECOMPUTE – When would anyone want to use it?

HTH

Delegates, Invoke, InvokeRequired

Question: What is InvokeRequired? Why this word is so difficult and what is it do? 

Answer: InvokeRequired is a property of a control which tells whether or not you can safely access the control. It is a boolean to check if you are on the UI thread before you try to update a form or control from a worker thread. 

If the property is True, then an invocation is required to access the control as the caller is on different thread than the one that owns the control's handle.

The invocation is performed by calling the control's Invoke or BeginInvoke method. 
You create a delegate, which is an object that contains the reference to a method. Then we pass this delegate to Invoke or BeginInvoke method which essentially call the reference method again but on thread that owns the control's handle.

Summary:
InvokeRequired asks 'Am I on the right thread?', if so carry on, else I need a delegate.

I got help and understanding of this from: 

Accessing Controls from Worker Threads

HTH.

Insert Data in DataGridView

Hi,

Lets say we already have DataGridView control as 'dgView' defined on our form with our columns defined as  FirstName, LastName and Address.
All columns were added from Design view of the form.
Now in code behind, if we just to add row without binding it to some datasource, it would be:
 

dgView.Rows.Add(New String() {"John","Doe","123 Main St, City UK"})

 

If we want to bind it with dataset or datatable then it would be :

 

Dim dt As New DataTable
dt.Columns.Add("FirstName") dt.Columns.Add("LastName") dt.Rows.Add(New String() {"saqib", "mahmood"}) ' This property is set if we dont have predefined columns in DataGridView.
dgView.AutoGenerateColumns = True dgView.DataSource = dt

Happy Coding!

Delegates vb.net

Delegates are function pointers that store function address.

There are 3 steps to understand Delegates:

1. Defining Delegate
2. Instantiating Delegate
3. Assigning Address of function to Delegate

Nothing fancy; just memorize the above steps to absorb the whole idea.

'How to define?
Public Delegate Sub testfile(Byval filename As String)

'instantiating the delegate
Dim mytestfile As testfile

Private Sub DoWork()
    'now assign the address of function to the delegate

    mytestfile = AddressOf FileTester

    'it can be called as

    mytestfile("test.txt") 

    'or

    mytestfile.Invoke("test.txt")

End Sub

Public Sub FileTester(ByRef filename As String)
     MsgBox(filename)
End Sub

Now FileTester is really the function will be called which just shows the filename

Happy coding!