I have a problem with the following:
Dim sql As String = "SELECT ArithmeticScore FROM " & tablename & " WHERE DateAscending = " & todaysdate.ToString("%dd/mm/yyyy")
Using connection As New OleDbConnection(getconn)
Dim findscore As New OleDbCommand(sql, connection)
connection.Open()
Dim reader As OleDbDataReader = findscore.ExecuteReader() 'ERROR OCCURS HERE
While reader.Read()
If Not reader.IsDBNull(0) Then
scoreexists = True
MsgBox("score exists")
Else
scoreexists = False
MsgBox("score does not exist")
End If
End While
reader.Close()
connection.Close()
End Using
I want to check if the cell in ArithmeticScore is empty when DateAscending = todaysdate
getconn Holds the connection string, tablename holds the name of the table.
I'm getting the error: 'Division by zero'
I understand why the program can't do that, but why on earth would it? I'm only trying to find out if a cell has a value in it or if its empty. The cell in question does have a value, 51.606 as a Decimal. I'm using an access database.
Related
Ive been wrestling with the code below for a long time now, and just when i thought it works it doesnt, and it doesnt even give me an error.
Dim sql As String = "UPDATE " & table & " SET ArithmeticScore = #score WHERE DateAscending = " & todaysdate
Using connection As New OleDbConnection(conn)
Using command As New OleDbCommand(sql, connection)
connection.Open()
command.Parameters.Add("#score", OleDbType.Decimal).Value = score
MsgBox("score was added = " & score)
command.ExecuteNonQuery()
connection.Close()
End Using
End Using
todaysdate currently holds the value 27/04/2020 as date
conn holds the connection string, table holds the table name.
The messagebox outputs what it is meant to, with score having a decimal value that should be added into the table.
The purpose of this code is to update the ArithmeticScore column in the table, Where DateAscending = 27/04/2020. When the program is finished, and i check the database, the cell remains blank. Why could this be?
This is because executed query can not find required record.
Try to set correct type for sql parameter for DateAscending column.
Dim sql As String =
$"UPDATE {table} SET ArithmeticScore = #score WHERE DateAscending = #todaysdate"
Using connection As New OleDbConnection(conn)
Using command As New OleDbCommand(sql, connection)
command.Parameters.Add("#score", OleDbType.Decimal).Value = score
command.Parameters.Add("#todaysdate", OleDbType.Date).Value = DateTime.Now.Date
connection.Open()
Dim affectedRows As Integer = command.ExecuteNonQuery()
' Check or display that affectedRows is greater than zero
End Using
End Using
i confused why mySqlDataReader.Read stuck on the last record and doesnt EOF ..
Here's my private function for executeSql :
Private Function executeSQL(ByVal str As String, ByVal connString As String, ByVal returnRecordSet As Boolean) As Object
Dim cmd As Object
Dim objConn As Object
Try
If dbType = 2 Then
cmd = New MySqlCommand
objConn = New MySqlConnection(connString)
Else
cmd = New OleDbCommand
objConn = New OleDbConnection(connString)
End If
'If objConn.State = ConnectionState.Open Then objConn.Close()
objConn.Open()
cmd.Connection = objConn
cmd.CommandType = CommandType.Text
cmd.CommandText = str
If returnRecordSet Then
executeSQL = cmd.ExecuteReader()
executeSQL.Read()
Else
cmd.ExecuteNonQuery()
executeSQL = Nothing
End If
Catch ex As Exception
MsgBox(Err.Description & " #ExecuteSQL", MsgBoxStyle.Critical, "ExecuteSQL")
End Try
End Function
And this is my sub to call it where the error occurs :
Using admsDB As MySqlConnection = New MySqlConnection("server=" & rs("server") & ";uid=" & rs("user") & ";password=" & rs("pwd") & ";port=" & rs("port") & ";database=adms_db;")
admsDB.Open()
connDef.Close()
rs.Close()
'get record on admsdb
Dim logDate As DateTime
Dim str As String
str = "select userid, checktime from adms_db.checkinout in_out where userid not in (select userid " &
"from adms_db.checkinout in_out join (select str_to_date(datetime,'%d/%m/%Y %H:%i:%s') tgl, fid from zsoft_bkd_padang.ta_log) ta " &
"on ta.fid=userid and tgl=checktime)"
Dim rsAdms As MySqlDataReader = executeSQL(str, admsDB.ConnectionString, True)
Dim i As Integer
'This is where the error is, datareader stuck on the last record and doesnt EOF
While rsAdms.HasRows
'i = i + 1
logDate = rsAdms(1)
'save to ta_log
str = "insert into ta_log (fid, Tanggal_Log, jam_Log, Datetime) values ('" & rsAdms(0) & "','" & Format(logDate.Date, "dd/MM/yyyy") & "', '" & logDate.ToString("hh:mm:ss") & "', '" & logDate & "')"
executeSQL(str, oConn.ConnectionString, False)
rsAdms.Read()
End While
'del record on admsdb
str = "truncate table checkinout"
executeSQL(str, admsDB.ConnectionString, False)
End Using
i'm new to vbnet and really have a little knowledge about it,, please help me,, and thank you in advance..
The issue is that you're using the HasRows property as your loop termination expression. The value of that property never changes. Either the reader has rows or it doesn't. It's not a check of whether it has rows left to read, so reading has no effect.
You are supposed to use the Read method as your flag. The data reader begins without a row loaded. Each time you call Read, it will load the next row and return True or, if there are no more rows to read, it returns False.
You normally only use HasRows if you want to do something special when the result set is empty, e.g.
If myDataReader.HasRows Then
'...
Else
MessageBox.Show("No matches found")
End If
If you don't want to treat an empty result set as a special case then simply call Read:
While myDataReader.Read()
Dim firstFieldValue = myDataReader(0)
'...
End While
Note that trying to access any data before calling Read will throw an exception.
I am Trying to create a login form for my software and i keep getting this feedback as error; "There are no rows at postion 0".....This happens whenever i try to add a WHERE clause to my (SLELECT ProfileName, ProfilePassword from Profile) query (i.e 'sqlQuery' in code)......This is a snippet of my code
Public Sub sql_login(ByVal sqlQuery As String)
Try
'OPENING THE CONNECTION
con.Open()
'INITIALIZE YOUR COMMANDS
'IT HOLDS THE DATA TO BE EXECUTED
With cmd
'PASS ON THE VALUE OF CON TO THE MYSQL COMMANND WHICH IS THE CONNECTION
.Connection = con
'THE FUNCTION OF THIS IS TO RETURN THE TEXT REPRESENTED BY A COMMAND OBJECT
.CommandText = sqlQuery
End With
Dim dt = New DataTable
'FOR RETRIEVING AND FILLING DATA IN THE TABLE
Dim da = New SqlDataAdapter(sqlQuery, con)
'NEW TABLE IN THE DATATABLE
da.Fill(dt)
con.Close()
'SET THE TOTAL ROWS OF THE TABLE IN A VARIABLE[MAXROWS]
Dim maxrows As Integer = dt.Rows.Count
con.Close()
'preventing non empty values
If Loginform.UsernameTextBox.Text <> "" And Loginform.PasswordTextBox.Text <> "" Then
If dt IsNot Nothing Then
'CHECKING IF THE TOTAL ROWS OF THE TABLE ARE GREATER THAN 0
If maxrows > 0 Then
'THIS WILL BE NOTIFY YOU THAT WHO WOULD BE THE USER'S
MessageBox.Show("Welcome " & dt.Rows(1).Item(0) & "!" & ControlChars.NewLine & "You have sucessfully logged in.", "Login Confirmation")
'Tracing login time
Try
cmd.CommandType = System.Data.CommandType.Text
cmd.CommandText = "INSERT INTO ProfileDates (ProfileName, LoginDates, ProfileID) VALUES ('" & Loginform.UsernameTextBox.Text & "',GetDate(),( SELECT TOP 1 profileID FROM Profile where ProfileName = '" & Loginform.UsernameTextBox.Text & "') )"
cmd.Connection = con
con.Open()
cmd.ExecuteNonQuery()
con.Close()
Suppliers_Module.LogoutBtn.Enabled = True
Suppliers_Module.LoginButton.Enabled = False
Catch ex As Exception
con.Close()
MessageBox.Show(ex.Message)
End Try
end if
end if
end if
counting on you for your help. Thanks in advance!
I'm trying to pull data from ACCESS database.
As it is, the code works, and gives no errors...
However, I can't seem to be able to display a messagebox if the record doesn't exist. It simply returns an empty string.
Using dbCon = New OleDbConnection("Provider=Microsoft.ACE.OLEDB.12.0;" & "Data Source = '" & Application.StartupPath & "\Res\T500G.accdb'")
dbCon.Open()
Dim Query1 As String = "SELECT SUM(Total) FROM [T500] WHERE Pro=#Pro"
Dim cmd1 As OleDb.OleDbCommand = New OleDbCommand(Query1, dbCon)
cmd1.Parameters.AddWithValue("#Pro", ComboBoxBP.SelectedItem.ToString)
Dim reader As OleDb.OleDbDataReader
reader = cmd1.ExecuteReader
While reader.Read()
TextBox1.Text = reader.GetValue(0).ToString
End While
reader.Close()
dbCon.Close()
End Using
I've tried using If reader.hasrows then display result in textbox, else show messagebox etc, but it doesn't work.
If reader.HasRows Then
While reader.Read()
TextBox1.Text = reader.GetValue(0).ToString
End While
Else
MessageBox.Show("asd")
End If
If I remove the .ToString from reader.GetValue(0) I get an error if the selected item from the combobox doesn't exist in the database. Cannot convert DBNull to integer or something.
So my question is, how to display a messagebox if the record "#Pro" doesn't exist?
Thanks~
Fixed(Workaround) with this
Dim ValueReturned As String
While reader.Read()
ValueReturned = reader.GetValue(0).ToString
If ValueReturned = "" Then
MessageBox.Show("Not Found", "Error", MessageBoxButtons.OK, MessageBoxIcon.Error)
Else
MetroTextBox1.Text = ValueReturned
End If
End While
Using OleDbDataReader is suboptimal for your query because it is never going to return a set of records to traverse:
Dim sql = "SELECT SUM(...=#p1"
' rather than sprinkling you connection string all over
' the app, you can make a function returning one
Using conn As OleDbConnection = GetConnection(),
cmd As New OleDbCommand(sql, GetConnection())
conn.Open())
' ToDo: Check that ComboBoxBP.SelectedItems.Count >0 before this
cmd.Parameters.AddWithValue("#p1", ComboBoxBP.SelectedItem.ToString)
' execute the query, get a result
Dim total = cmd.ExecuteScalar
' if there is no matches, OleDb returns DBNull
If total Is System.DBNull.Value Then
' no matches
MessageBox.Show("No matching records!"...)
Else
MessageBox.Show("The Total is: " & total.ToString()...)
End If
End Using ' disposes of the Connection and Command objects
Alteratively, you could use If IsDBNull(total) Then.... If you want, you can also convert it:
Dim total = cmd.ExecuteScalar.ToString()
' DBNull will convert to an empty string
If String.IsNullOrEmpty(total) Then
MessageBox.Show("No Soup For You!")
Else
...
End If
You could change your query to (this is for SQL-Server):
IF EXISTS (SELECT * FROM [T500] WHERE Pro = #Pro) SELECT SUM(Total) FROM [T500] WHERE Pro = #Pro ELSE SELECT 'Not Found'
And change your code to:
Dim ValueReturned As String
While reader.Read()
ValueReturned = reader.GetValue(0).ToString
End While
If ValueReturned Is Nothing OrElse ValueReturned = "Not Found" Then
MessageBox.Show("Not Found", "Error", MessageBoxButtons.OK, MessageBoxIcon.Error)
Else
TextBox1.Text = ValueReturned
End If
I want to show all the data in a specific column in one combobox and my code is just showing the last data in the column here is the code i am using
Dim connectionstring As String = "Data Source=localhost\SQLEXPRESS;InitialCatalog=Enginee;Integrated Security=True"
Try
Dim connection As New SqlClient.SqlConnection(ConnectionString)
Dim sqlquery As String
connection.Open()
MessageBox.Show("Open")
sqlquery = " Select PROJECT.PROJECT_CODE,PROJECT.PROJECT_NAME From PROJECT INNER JOIN ENGINEERS on ENGINEERS.ENGINEER_ID = ENGINEERS.ENGINEER_ID where ENGINEERS.FNAME = '" & Sign_In.TextBox1.Text & "' "
Dim selectcommand As New SqlClient.SqlCommand(sqlquery, connection)
Dim reader As SqlClient.SqlDataReader = selectcommand.ExecuteReader
Dim test As Boolean = reader.Read
While test = True
ComboBox1.Text = reader(0)
TextBox1.Text = reader(1)
test = reader.Read
End While
Catch ex As Exception
MessageBox.Show("Failed")
End Try
Instead of setting the .text of the ComboBox add the item.
ComboBox1.Items.Add(reader(0));
Setting the Text value will just set what the current item is, not adding them to the dropdown list.