When I run the following SQL statement in SQL Server Management Studio it returns a count of 2
SELECT COUNT(*)
FROM Daisy_Copy2
WHERE ChargeCode = '1';
But for some reason when I run the following VB.net code the result variable returns a 0 and doesn't identify that duplicate codes exist.
Dim result As Integer
Using cmdb = New SqlCommand("SELECT COUNT(*) FROM Daisy_Copy2 WHERE ChargeCode = '1'", conn)
Int(result = cmdb.ExecuteScalar())
If result > 1 Then
MessageBox.Show("Duplicate Codes Exist!", "Billing", _
MessageBoxButtons.OK, MessageBoxIcon.Information)
Else
MsgBox(result)
End If
End Using
Can anyone help me understand why?
Any help greatly appreciated.
Instead of ExecuteNonQuery you should use ExecuteScalar
Dim result As Integer = CInt(cmd.ExecuteScalar())
ExecuteNonQuery is normally used for updates or inserts that don't leave a result, so it returns an integer telling you how many rows were affected, not the result itself.
What you most likely are meaning to use is ExecuteScalar which returns the first column of the first row in the result set returned by the query, in this case the integer containing your count.
this is just a way you can use:
Dim Sqlda = New SqlDataAdapter("SELECT COUNT(*) AS tCount FROM Daisy_Copy2 WHERE ChargeCode=1", conn)
Dim sqlds = New DataSet
Sqlda.Fill(sqlds, "Daisy_Copy2")
Dim tblRow As DataRow
For Each tblRow In sqlds.Tables("Daisy_Copy2").Rows
MsgBox(tblRow("tCount").ToString())
Next
use below link to read more about it
System.Data.SqlClient Namespace
Good luck
Related
net and would to have the Header Text of columns in a datagridview be named after results from the database, e.g the query in my code returns four dates,30/08/2017,04/09/2017,21/09/2017 and 03/02/2018. My aim is to have the column headers in the data grid named after those dates. Your help will highly be appreciated.
sql = "SELECT COUNT (ServiceDate) As NoOfServiceDates FROM (SELECT DISTINCT ServiceDate FROM tblattendance)"
Using command = New OleDbCommand(sql, connection)
Using reader = command.ExecuteReader
reader.Read()
ColumnNo = CInt(reader("NoOfServiceDates")).ToString
End Using
End Using
DataGridView1.ColumnCount = ColumnNo
For i = 0 To DataGridView1.Columns.Count - 1
sql = "SELECT DISTINCT ServiceDate FROM tblattendance"
Using command = New OleDbCommand(sql, connection)
Using reader = command.ExecuteReader
While reader.Read
DataGridView1.Columns(i).HeaderText = reader("ServiceDate").ToString
End While
End Using
End Using
Next
The current code re-runs the query each time through the column count loop, meaning it will set the column header for that column to all of the date values in sequence, so the last value in the query shows in the all the columns. You only need to run the query once:
Dim i As Integer = 0
sql = "SELECT DISTINCT ServiceDate FROM tblattendance"
Using command As New OleDbCommand(sql, connection), _
reader As OleDbDatareader = command.ExecuteReader()
While reader.Read
DataGridView1.Columns(i).HeaderText = reader("ServiceDate").ToString
i+= 1
End While
End Using
Additionally, this still results in two separate trips to the database, where you go once to get the count and again to get the values. Not only is this very bad for performance, it leaves you open to a bug where another user changes your data from one query to the next.
There are several ways you can get this down to one trip to the database: loading the results into memory via a List or DataTable, changing the SQL to include the count and the values together, or adding a new column each time through the list. Here's an example using the last option:
DataGridView1.Columns.Clear()
Dim sql As String = "SELECT DISTINCT ServiceDate FROM tblattendance"
Using connection As New OleDbConnection("string here"), _
command As New OleDbCommand(sql, connection)
connection.Open()
Using reader As OleDbDataReader = command.ExecuteReader()
While reader.Read
Dim column As String = reader("ServiceDate").ToString()
DataGridView1.Columns.Add(column, column)
End While
End Using
End Using
Even better if you can use something like Sql Server's PIVOT keyword in combination with the DataGridView's AutoGenerateColumns feature for DataBinding, where you will write ONE SQL statement that has both column info and data, and simply bind the result set to the grid.
The For Next is incorrect. You execute your command for every column, when you only need to execute it once. The last result from the DataReader will be the header for every column as currently written.
You should iterate through your DataReader and increment the cursor variable there:
Dim i As Integer = 0
Using command = New OleDbCommand(sql, connection)
Using reader = command.ExecuteReader
While reader.Read
DataGridView1.Columns(i).HeaderText = reader("ServiceDate").ToString
i += 1
End While
End Using
End Using
I don't know how to find if the where statement occurred in the code when I execute it:
Dim cmd2 As SqlCommand = New SqlCommand("
UPDATE ShTb
SET Email=#EmailAddress,
Temp=#temp,
TEL=#telnum,
TempTime=#temptime
WHERE ShID=#SharjID", con1)
cmd2.Parameters.AddWithValue("#EmailAddress", EmailAddress)
cmd2.Parameters.AddWithValue("#SharjID", SharjID)
cmd2.Parameters.AddWithValue("#temp", temp)
cmd2.Parameters.AddWithValue("#telnum", telnum)
cmd2.Parameters.AddWithValue("#temptime", temptime)
con1.Open()
cmd2.ExecuteNonQuery()
con1.Close()
I assume you want to know if any rows were effected by the update.
You can do this by checking the return value of ExecuteNonQuery
Dim rowsEffected = cmd2.ExecuteNonQuery()
if rowsEffected > 0 Then
'One or more rows were changed
End if
ExecuteNonQuery returns the number of rows affected by the command.
For UPDATE, INSERT, and DELETE statements, the return value is the number of rows affected by the command. (MSDN)
dim r1 as int
r1=cmd2.ExecuteNonQuery()
If r1 > 0 --one, or more rows were affected....
This is the code that tries to grab the largest StockID from the database (Access database) , but my problem is that it generates StockID's up to "S10", after this it simply doesn't increment any further. This is the subroutine that generates the StockID:
Sub generate_Stock_ID()
Dim Stock_start As String = "S"
Dim Stock_Gen As String = "SELECT MAX(StockID) FROM tblStock WHERE StockID LIKE '" & Stock_start & "%%%' "
Dim da As OleDbDataAdapter = New OleDbDataAdapter(Stock_Gen, conn)
Dim ds As DataSet = New DataSet
da.Fill(ds, "StockID")
Dim dt As DataTable = ds.Tables("StockID")
Dim count As Integer = ds.Tables("StockID").Rows.Count
If ds.Tables("StockID").rows.count = 0 Then
StockID = "S1"
Else
StockID = ds.Tables("StockID").Rows(0).Item(0)
StockID = StockID.Substring(1, (StockID.Length - 1))
StockID = Stock_start & (StockID + 1)
End If
End Sub
Screenshot of my database
Note* there are multiple ID's for various other subroutines which all share the same incrementation issue, so if i fix this i fix the other ones too. So at the moment i think my problem lies in the syntax of my SQL statement, but im open to suggestions.
Thanks!
Don't treat an Integer as String. Otherwese MAX or ORDER BY will use lexicographical instead of numerical order which means that S11 is "lower" than S2.
So you should make this column an int-column and prepend S only where you display it. Then MAX(StockID) returns an Integer, you just have to cast it and add 1:
Using conn As New OleDbConnection("Connection-String")
Using cmd As New OleDbCommand(Stock_Gen, conn)
conn.Open()
Dim stockIDObj As Object = cmd.ExecuteScalar()
If stockIDObj IsNot Nothing Then
Dim maxStockId As Int32 = DirectCast(stockIDObj, Int32)
maxStockId += 1
' ...... '
End If
End Using
End Using
You should also change OPTION STRICT to ON. Then this would never compile since the same variable cannot be used for an Object, String and Integer which is very good since it prevents errors.
If you want to keep it as string you have to cast the substring always in the database which is less readable and less efficient. I also don't know how to do it in access.
If you want to change the type of column in an already populated table you should first add a new column with a similar name which is of type int. If all have S at the beginning you could first remove that, then you can update the new column with the casted int value. Finally you can delete the old column and rename the new to the old.
The root of this issue that StockID is a STRING and 'S1'>'S10' so for all StockId > 10 you get max = 'S1'.
As a fast fix try to change MAX(StockID) to:
SELECT 'S'+CAST(MAX(CAST(SUBSTRING(StockID,2,100) as int)) as varchar(100))
For ACCESS DB try to use:
SELECT "S" & cstr(MAX(CINT(MID(StockID,2,100))))
I am trying to run the following code converting my datatable to be usable in linq all seems fines and compiles but when I Execute the statement I get the following statement i get the error below new entires just has location and ordernumber in the return values I have to do it this way as I am supporting a legacy access 97 system thanks.
Dim total = From row In newEntries.AsEnumerable()
Select row.Field(Of Int32)("location") Distinct
retVal = Convert.ToInt32(total)
This is my whole code but im still getting an invalid type cast error their is data exsits for this order by teh way
Dim retVal As Int32
Dim newEntries As New DataTable
Dim script As String = scriptBuilder.GetDistinctOrdersForLocations(OrderNumber)
newEntries = connection.SqlSelectToDataTable(script)
Dim total = From row In newEntries.AsEnumerable()
Select row.Field(Of Int32)("location") Distinct
retVal = total.Count()
If you want the count of the collection just do this:
retVal = total.Count()
this will return the count from the distinct query that you have written.
Just to clarify, #David B identified the data type of location was int16 not int32, so changing this in the linq query resolved the issue.
Your LINQ query is returning a collection. You should use something like First or FirstOrDefault.
I'm a little rusty on VB LINQ, but try :
retVal = Convert.ToInt32(total.First())
Note: This will throw an error if there are no items in the collection.
It's important to understand when you write a LINQ query and assign it to a variable, that variable essentially contains a query object, and not the results of running the query. In order to get the value that results from the query, you need to call some method on the query object such as:
total.Single() ' Assumes you expect the query to return exactly one result.
I changed the code to int16 worked here is the code for any one else stuck thanks #Ric
Dim retVal As Int32
Dim newEntries As New DataTable
Dim script As String = scriptBuilder.GetDistinctOrdersForLocations(OrderNumber)
newEntries = connection.SqlSelectToDataTable(script)
Dim total = From row In newEntries.AsEnumerable()
Select row.Field(Of Int16)("location") Distinct
retVal = total.Count()
In my .NET application I have to get results from a MS Access database. I would like to add error checking to make sure a row was returned from my SELECT statement.
How can I make sure a result was returned?
Thank you.
Dim mySelectCommand As New OleDbCommand("SELECT * FROM SomeTable")
Dim myReader As OleDbDataReader = mySelectCommand.ExecuteReader()
If Not myReader.HasRows Then
'No row has been returned'
End If