I have an Access table which has a Number field and a Text field.
I can run a query like this:
SELECT * FROM Table ORDER BY intID ASC
//outputs 1,2,3,10
But when I try to run the same query through the .NET OleDB client, like this:
Private Sub GetData()
Using cnDB As New OleDbConnection("Provider=Microsoft.Jet.OLEDB.4.0;Data Source=" & Path)
cnDB.Open()
Dim SQL As String = "SELECT * FROM Table ORDER BY intID ASC"
Dim cmd As New OleDbCommand(SQL, cnDB)
Dim dr As OleDbDataReader = cmd.ExecuteReader()
While dr.Read()
lst.Items.Add(dr.Item("intID") & " - " & dr.Item("strName"))
End While
cnDB.Close()
End Using
End Sub
I get items in the order 1,10,2,3.
What's going on here, and how can I have the data sort "naturally" (1,2,3,10) in both places?
try
SELECT * FROM Table ORDER BY CInt(intID) ASC
to explicitly tell Access to treat this as an integer and not a string. Obviously, something in the OleDbClient is seeing this field as a string (text field) and sorting accordingly.
I suspect the problem is your connection string. If you're connecting to an Access database and include IMEX=1 in your connection string, the provider will treat all data as string. As such, the ordering will order by the string value, giving you 1, 10, 2, 3, as opposed to leaving the intID as an integer, and ordering it in numerical order.
It looks like you're getting a lexical (alphabetic) order. This will be correct if something in your database or query thinks that is a varchar/text column type instead of a numeric type.
Related
I am trying to find the max product ID and store the value in a local variable "MaxID" and return this value. I am trying to convert the result of the query into an Integer type but I am not able to do it. Below is the code:
Public Function GetMaxID(ByVal TableName As String, ByVal ID As String) As Integer
Dim MaxID As Integer
Dim sqlquery As SqlCommand
Dim field_name As String = ID
Dim con As SqlConnection
con = New SqlConnection()
con.ConnectionString = "Data Source=(LocalDB)\MSSQLLocalDB;AttachDbFilename='D:\Docs Dump\Work\Srinath\SrinathDB.mdf';Integrated Security=True;Connect Timeout=30"
con.Open()
Try
sqlquery = New SqlCommand("SELECT MAX( #field ) FROM #table ", con)
sqlquery.Parameters.AddWithValue("#field", field_name)
sqlquery.Parameters.AddWithValue("#table", TableName)
MaxID = CInt(sqlquery.ToString)
con.Close()
Return MaxID
Catch ex As Exception
Return 0
Exit Function
con.Close()
End Try
End Function
End Class
MaxID = CInt(sqlquery.ExecuteScalar())
You also should know about SqlCommand.ExecuteReader(), SqlCommand.ExecuteNonQuery() (for inserts/updates/deletes), and SqlDataAdapter.Fill().
Where you'll still have a problem is you can't use a parameter value for the table name or column name. The Sql Server engine has a "compile" step, where it has to be able to work out an execution plan, including permissions/security, at the beginning of the query, but variable names like #table and #field aren't resolved until later. It's not what actually happens, but think of it as if you had string literals in those places; imagine trying to run this:
SELECT MAX('ID') FROM 'MyTable'
MAX('ID') will always return the string value ID, and not anything from an ID column in any rows. But the MyTable part is not the correct place for a string literal, and such a query wouldn't even compile.
I also see people here from time to time try to create functions like GetMaxId(), and it's almost always misguided in the first place. If the intended use for this function is the same as what I usually see, you're setting up a major race condition issue in your application (one that probably won't show up in any testing, too). Sql Server gives you features like identity columns, sequences, and the scope_identity() function. You should be using those in such a way that new IDs are resolved on the server as they are created, and only (and immediately) then returned to your application code.
But that issue aside, here's a better way to structure this function:
Public Class DB
Private conString As String = "Data Source=(LocalDB)\MSSQLLocalDB;AttachDbFilename='D:\Docs Dump\Work\Srinath\SrinathDB.mdf';Integrated Security=True;Connect Timeout=30"
'You want a separate method per-table that already knows the table and column names
Public Function GetMyTableMaxID() As Integer
Dim sql As String = "SELECT MAX(ID) FROM MyTable"
Using con As New SqlConnection(conString), _
sqlQuery As New SqlCommand(sql, con)
'Parameters would go here.
'Do NOT use AddWithValue()! It creates performance issues.
' Instead, use an Add() overload where you provide specific type information.
'No exception handling at this level. The UI or business layers are more equipped to deal with them
con.Open()
Return CInt(sqlQuery.ExecuteScalar())
End Using
'No need to call con.Close()
'It was completely missed in the old code, but handled by the Using block here
End Function
End Class
As the title says, I'm unable to filter an SQL sentence from access database with vb.net
Dim data1 As String = DateTimePicker1.Value.ToShortDateString
Dim data2 As String = DateTimePicker2.Value.ToShortDateString
Dim sql As String = "SELECT totais.* From totais Where totais.data Between #" + data1 + "# And #" + data2 + "#;"
It gives me random values. If i put 1-10(October)-2019 it gives me all the records in system, if i put 12-10(October)-2019 it only gives today's record (doesn't show yesterday and before records). I'm not finding the problem, can you please help?
Thanks
I would use Parameters instead of concatenating a string for the Sql statement. It makes the statement much easier to read and avoids syntax errors.
With OleDb the order that parameters appear in the sql statement must match the order they are added to the parameters collection because OleDb pays no attention to the name of the parameter.
Private Sub OPCode()
Dim sql As String = "SELECT * From totais Where data Between #StartDate And #EndDate;"
Using dt As New DataTable
Using cn As New OleDbConnection("Your connection string"),
cmd As New OleDbCommand(sql, cn)
cmd.Parameters.Add("#StartDate", OleDbType.Date).Value = DateTimePicker1.Value
cmd.Parameters.Add("#EndDate", OleDbType.Date).Value = DateTimePicker2.Value
cn.Open()
dt.Load(cmd.ExecuteReader)
End Using
DataGridView1.DataSource = dt
End Using
End Sub
You need to use single quotes and convert type in SQL like this:
SELECT totais.* FROM totais WHERE totais.data Between CDATE('" + data1 + "') And CDATE('" + data2 + "');"
You should use parameters as per Mary's answer BUT for completeness...
Ms/Access requires dates specified as #mm/dd/yy# so your SQL will only work properly where the local date time format is mm/dd/yy. i.e. mostly the US. Otherwise you will have to format your date string.
I'm a beginner. I created a database in vb.net and I need to build a query, in the SQL Statement - Table Adapter, which returns records even if parameters are NULL in one or more textbox. To be clear, I have several textboxes (related to fields) with which I can filter record results and I want to refine my research as much as I fill textboxes, reverse if I fill just one of them randomly.
Sorry if I confused you, but I guess you get it anyway.
In its simplest form (assuming SQL server param concepts)
-- Define your columns to pull back/display
select t1.column1, t1.column2, t1.column3...
-- Define the table, give it an alias if you're using more than one or it has a silly name
from thetable t1
-- Apply filters
where
-- For each textbox/column search combo, do this...
(column1 = #field1 or #field1 is null)
or -- If the filter is restrictive, use AND here
(column2 = #field2 or #field2 is null)
or -- If the filter is restrictive, use AND here
...
I would dump the table adapter for this requirement.
I am building the sql string using a StringBuilder. StringBuilder objects are mutable, String is not.
To run this Code
1. I assumed Sql Server. If this is not the case change all the data object (Connectio and Command) to the proper provider.
Add your connection string to the constructor of the connection.
Add your table name where it says "YourTable"
I just used TextBox1 etc. as control names. Use your actual control names
Replace Field1, Field2 etc. with your actual column names.
The parameter names (by convention, they start with #) can be anything you want as long as they match the name you add to the Parameters collection.
You will have to check your database for the actual datatypes of the fields. Be sure to convert the TextBox values to the compatible type. TextBox.Text is a string so it will be compatible to .VarChar but note number types or dates.
I added a Debug.Print to check what the Sql string looks like. Be cautious about where I have spaces when building the string. You can see the result in the immediate window (available from Debug menu).
If you don't already have a DataGridView on your form, add one so you can see the reults of your query.
Finally, always use parameters, use Using...End Using blocks, and open your connection at the last minute.
Private Sub RunDynamicQuery()
Dim sb As New StringBuilder
Dim AndNeeded As Boolean
Dim dt As New DataTable
Using cn As New SqlConnection("Your connection string")
Using cmd As New SqlCommand
sb.Append("Select * From YourTable Where ")
If Not String.IsNullOrEmpty(TextBox1.Text) OrElse Not String.IsNullOrWhiteSpace(TextBox1.Text) Then
sb.Append("Field1 = #Field1")
cmd.Parameters.Add("#Field1", SqlDbType.Int).Value = CInt(TextBox1.Text)
AndNeeded = True
End If
If Not String.IsNullOrEmpty(TextBox2.Text) OrElse Not String.IsNullOrWhiteSpace(TextBox2.Text) Then
If AndNeeded Then
sb.Append(" And")
End If
sb.Append(" Field2 = #Field2")
cmd.Parameters.Add("#Field2", SqlDbType.VarChar).Value = TextBox2.Text
AndNeeded = True
End If
If Not String.IsNullOrEmpty(TextBox3.Text) OrElse Not String.IsNullOrWhiteSpace(TextBox3.Text) Then
If AndNeeded Then
sb.Append(" And")
End If
sb.Append(" Field3 = #Field3")
cmd.Parameters.Add("#Field3", SqlDbType.VarChar).Value = TextBox3.Text
AndNeeded = True
End If
sb.Append(";")
cmd.Connection = cn
Debug.Print(sb.ToString)
cmd.CommandText = sb.ToString
cn.Open()
dt.Load(cmd.ExecuteReader)
End Using
End Using
DataGridView1.DataSource = dt
End Sub
I'm doing a connection with excel and I have a problem when I try to use an ID that have 0 behind...
I'm using a ListBox and add the IDs from the excel's worksheet as items. IDs have 9 numbers, like "123456789" or "098765430". So that I remove the last 4 characters to search the IDs with the same 5 numbers and add in another ListBox. It works fine, except with the codes with 0 (zero) behind.
Dim ConnectionString As New OleDbConnection("Provider=Microsoft.ACE.OLEDB.12.0; Data Source=" & Application.StartupPath & "\Tabela_Precos.xlsx; Extended Properties=Excel 12.0;")
ConnectionString.Open()
Dim ds As New DataSet
Dim dt As New DataTable
ds.Tables.Add(dt)
Dim da
For i = 0 To Form1.ListBox1.Items.Count - 1
Dim str As String = Compras.ListBox1.Items(i).ToString
Dim prod As String = str.Remove(str.Length - 4)
da = New OleDbDataAdapter("SELECT * FROM [Sheet1$] WHERE ID like '%" & prod & "%'", ConnectionString)
ListBox1.Items.Add(dt.Rows(i).Item(0))
Next
Your Excel file has the ID column entered as integer values, but is formatted for left-zero padding to present as a nine character field. Your Excel db connection is reading the values as numbers (type Double, even-though they are integers). Your original select statement is implicitly convert ID to a string for the Like comparison; however, this conversion does not now you want left-zero padding. To use this type of comparison, you need to format ID yourself.
Select * From [sheet1$] Where (Format([ID], ""000000000"") Like '" & prod & "%')"
As you have indicated in the comments above, this works. However, it is not the most efficient in terms of speed. Since ID is numeric, it should be faster to do a numeric comparison. You have already defined a String variable named prod and the following solution uses that variable to prepare a numeric value for use in constructing an alternate select based on your criteria.
Dim prodNum As Int32 = Int32.Parse(prod) * 10000I
Then the Select statement would become:
"Select * From [sheet1$] Where ((([ID]\10000) * 10000)=" & prodNum.ToString & ")"
These examples use a concatenated select statement, and ideally you would not do it this way, but rather use a parameterized statement with replacement values. I'll leave that exercise up to you to perform.
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))))