Finding Missing numbers in a given range - vb.net

Question

So i have a problem with my codings and was wondering if anyone can help me.
Basically i'm using VB.NET and MSSQL to make a program on finding missing numbers in between a given range set by the user. The program will read from the table and give the output on a textbox. And the above codes are so far what i can come up with. But the problem is, i get wrong output and not what i want. Here's an image of the output.
Function FindingMissingNumber() As String
Dim intX As Integer = Nothing
Dim intY As Integer = Nothing
Dim strSting As String = Nothing
Dim strSqlQUery As String = Nothing
Dim cmdSqlCommand As Data.SqlClient.SqlCommand = Nothing
Dim rdrDataReader As Data.SqlClient.SqlDataReader = Nothing
'------------------------------------------------------------------------------------------------------------------------
'-> Process
'------------------------------------------------------------------------------------------------------------------------
strSqlQUery = "Select ExReportPolicyNo From DBReport Order by ExReportPolicyNo"
Dim msSqlConnection As New Data.SqlClient.SqlConnection()
'NOTE - You may need to CHECK your connection string!!! in the line below
msSqlConnection.ConnectionString = "Data Source=SISBSQL\SISBSQL;Initial Catalog=ExceptionReport;User ID=sa;Password=123;"
cmdSqlCommand = New Data.SqlClient.SqlCommand(strSqlQUery, msSqlConnection)
If cmdSqlCommand.Connection.State = Data.ConnectionState.Closed Then cmdSqlCommand.Connection.Open()
rdrDataReader = cmdSqlCommand.ExecuteReader()
If rdrDataReader.HasRows Then
Do While rdrDataReader.Read()
intX = txtRangeLeft.Text
intY = txtRangeRight.Text
'intY = rdrDataReader.GetValue(rdrDataReader.GetOrdinal("ExReportPolicyNo"))
Do While intX <> intY
intX = intX + 1
If intX <> intY Then
strSting = strSting & intX & ", " 'if it is not, then record the non sequential number into the string
Else
Exit Do
End If
Loop
Loop
End If
If cmdSqlCommand.Connection.State = Data.ConnectionState.Open Then cmdSqlCommand.Connection.Close()
'return string
Return strSting
'tidy up
intX = Nothing
intY = Nothing
strSting = Nothing
strSqlQUery = Nothing
cmdSqlCommand = Nothing
rdrDataReader = Nothing
End Function
As you can see the program loops it multiple times, and give out the wrong output. The output should read only "286118, 286120, 286121". Question is where did i went wrong?

Answer 1

Try this (using linq)
Change query to return rows between start and end value
Select distinct ExReportPolicyNo From DBReport
Where ExReportPolicyNo between #start and #end
Order by ExReportPolicyNo
Create List from your query:
Dim originalList as List(Of Integer)
If rdrDataReader.HasRows Then
Do While rdrDataReader.Read()
originalList.Add(rdrDataReader.GetInt(0))
Loop
End If
Create List of range from your start and end number
//Dim rangeList = Enumerable.Range(286117, 286121 - 286117 + 1).ToList()
Dim starti = Int32.Parse(txtRangeLeft.Text)
Dim endi = Int32.Parse(txtRangeRight.Text)
Dim rangeList = Enumerable.Range(starti, endi - starti + 1).ToList()
Find all missing numbers
Dim missingList = originalList.Except(rangelist)
Create CSV string from list above
strString = String.Join(",", missingList.Select(x => x.ToString()).ToArray())