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- SQL Server to Access Database Table Export Program
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SQL Server to Access Database Table Export Program
Large companies tend to rely on many different types of databases, ranging in scale from a mainframe all the way down to a single-user database on an employee's PC. Frequently, new applications that require access to these databases appear, creating a complex web of dependencies between them. For example, a consultant may be hired to write an application that needs to read some data from an established SQL Server database. With ODBC, you can simply allow the consultant's application to attach to the database. However, this setup might pose a problem in certain situations:
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The SQL Server administrator now has to maintain additional login information for the new application.
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SQL Server performance may be negatively affected by the extra application.
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Changing the SQL Server tables accessed by the new application may require changing the application code, which will be difficult after the consultant is long gone.
An easy answer to these problems is to build an export file on an automated basis for the new program to use. An Access database is an ideal format for this export file because the program can use it just as it would the SQL Server.
Building the Sample Program
In case you have not noticed, I like to rely on INI files a lot. There's a reason for this: They can make your program more useful. This result should be especially apparent in this example because the INI file contains all the information the program needs to perform the export operation. You can compile the program once and use several INI files for different exports. It is intended to be a command-line utility, and is executed like this:
MDBMAKE C:\Data\REVENUE.INI MDBMAKE C:\Data\Employee.INI
The INI files themselves contain information that the program needs to connect to the SQL Server and create the Access tables. For example, entries specify the Access database (destination database) and the SQL Server connect string (source database):
DBFile=\\MYSERVER\PUBLIC\HRDATA\HRDATA.MDB SQLConnect="ODBC:DATABASE=personnel:uid=fred:pwd=garvin:DSN=MYSQLDB"
Next, the [Tables] section specifies the name and number of tables you want to create:
[Tables] Tables=4 Table1SQL=hrinfo Table1MDB=hrinfo Table1INI=hrinfo
Each table also contains a section that specifies the number and type of the fields in the table. For example, the hrinfo section might look like this:
[hrinfo] Fields=2 Fd1Name="EmployeeID" Fd1Type=DOUBLE Fd2Name="Name" Fd2Type=TEXT Fd2Size=40
While executing, the program uses For loops to browse through each section in the INI file because it needs the field information. For example, the hrinfo table created by the program has two fields: EmployeeID, which is of type Double, and Name, which is a 40-character text field.
Understanding the Sample Program
The SQL export program has just a few generic functions and no real user interface (other than a progress screen). The important functions are as follows:
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CreateLocalFile. Creates the database (MDB) file.
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CreateTable. Creates an empty table in the database.
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TransferTable. Transfers data from the SQL Server table to the new database.
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Main. Controls the flow of the program.
These functions are shown in Listing 23.3. Following the listing is an explanation of what happens during a sample program run.
Listing 23.3 Transferring Information from SQL to Access
'Important variables:
Dim dbLocal As Database 'Destination database (Access)
Dim dbSQL As Database 'Source database (MS SQL Server)
Dim sDBLocalPath As String 'Path to destination database
Dim sINIPath As String 'Path to INI File
Sub Main()
Dim sConnect As String 'SQL Server Connect String
Dim nTables As Integer 'Number of tables to transfer
Dim nCurTable As Integer 'Counter for current table
Dim sSQLTable As String 'Name of the SQL table
Dim sMDBTable As String 'Name of the Access table
Dim sSection As String 'INI file [Section]
Dim nCommand As Integer 'Commands can be run on the
Dim sCommand As String 'Access database (i.e. create index)
'GET INI FILE NAME
sINIPath = App.Path & "\SQLXPORT.ini"
If Trim$(Command$) <> "" Then sINIPath = Command$
'READ INFO FROM THE INI FILE
sDBLocalPath = sGetINIString(sINIPath, "General", "DBFile", "test.mdb")
sConnect = sGetINIString(sINIPath, "General", "SQLConnect", "ODBC;")
nTables = CInt(sGetINIString(sINIPath, "Tables", "Tables", "0"))
'SHOW FORM AND CONNECT TO SQL SERVER
frmWait.Show
frmWait.lblWait = "Connecting to SQL Server..."
DoEvents
On Error GoTo MainError
Set dbSQL = OpenDatabase("", False, True, sConnect)
'CALL FUNCTION TO CREATE MDB FILE
frmWait.lblWait = "Creating MDB file..."
DoEvents
CreateLocalFile
DoEvents
'CREATE TABLES IN THE NEW MDB FILE
For nCurTable = 1 To nTables
sSQLTable = sGetINIString(sINIPath, "tables", "table" & nCurTable & _
[ccc] "SQL", "none")
sMDBTable = sGetINIString(sINIPath, "tables", "table" & nCurTable & _
[ccc] "MDB", "none")
sSection = sGetINIString(sINIPath, "tables", "table" & nCurTable & _
[ccc] "INI", "none")
frmWait.lblWait = "Transferring " & sMDBTable
TransferTable sSQLTable, sMDBTable, sSection
Next nCurTable
'THE DATABASE HAS BEEN CREATED, RUN COMMANDS ON IT IF NECESSARY
nCommand = 0
sCommand = ""
While sCommand <> "?"
If nCommand <> 0 Then dbLocal.Execute sCommand
nCommand = nCommand + 1
sCommand = sGetINIString(sINIPath, "General", "Command" & nCommand, "?")
Wend
'CLOSE EVERYTHING DOWN AND END
frmWait.lblWait = "Disconnecting..."
dbLocal.Close
dbSQL.Close
Unload frmWait
DoEvents
End
MainError:
frmWait.Hide
Screen.MousePointer = vbDefault
WriteErrMsg "Main - Error " & Err & ": " & Error
End
Exit Sub
End Sub
Sub TransferTable(sSQLTable As String, sLocalTable As String, sSection As _
[ccc] String)
'This function transfers data from SQL server to an Access table
Dim rstemp As Recordset 'SQL recordset
Dim aTable As Recordset 'Access table
Dim nTemp As Integer ' Counter
Dim nFields As Integer ' variables
Dim nCount As Integer '
Dim sSQL As String 'SQL statement
Dim sTemp As String
On Error GoTo TRTError:
frmWait.ProgressBar1.Visible = True
nCount = 0
frmWait.ProgressBar1.Min = 0
'The user can either transfer a SQL table as-is,
'or the results of a query involving multiple tables.
'This next IF statement determines which and sets up the
'SQL statement- either "Select * from table" or the
'user-defined SQL statement.
sSQL = sGetINIString(sINIPath, sSection, "SQL", "")
If sSQL = "" Then
Set rstemp = dbSQL.OpenRecordset("Select Count(*) from " & sSQLTable, _
[ccc] dbOpenSnapshot, dbForwardOnly)
frmWait.ProgressBar1.Max = CInt(Trim$(" 0" & rstemp.Fields(0)))
rstemp.Close
DoEvents
Else
nTemp = 2
sTemp = sGetINIString(sINIPath, sSection, "SQL" & nTemp, "")
While sTemp <> ""
If sTemp <> "" Then sSQL = sSQL & sTemp
nTemp = nTemp + 1
sTemp = sGetINIString(sINIPath, sSection, "SQL" & nTemp, "")
Wend
frmWait.ProgressBar1.Max = 2000 'Set arbitrary value on progress bar
End If
'Actually open the recordset
If sSQL = "" Then
Set rstemp = dbSQL.OpenRecordset("Select * from " & sSQLTable, _
[ccc] dbOpenSnapshot, dbForwardOnly)
Else
Set rstemp = dbSQL.OpenRecordset(sSQL, dbOpenSnapshot, dbForwardOnly + _
[ccc] dbSQLPassThrough)
End If
'Open Local table
Set aTable = dbLocal.OpenRecordset(sLocalTable, dbOpenTable)
nFields = rstemp.Fields.Count - 1
'Transfer each record
While Not rstemp.EOF
aTable.AddNew
For nTemp = 0 To nFields
aTable.Fields(nTemp) = rstemp.Fields(nTemp)
Next nTemp
rstemp.MoveNext
nCount = nCount + 1
frmWait.ProgressBar1.Value = nCount
aTable.Update
Wend
rstemp.Close
aTable.Close
Exit Sub
TRTError:
WriteErrMsg "TRT-Error " & Err & ": " & Error
End
Exit Sub
End Sub
Sub CreateTable(ByRef tbl As TableDef, sTableName As String, sINISection As _
[ccc] String)
'This function creates an empty table in an Access database
Dim nFields As Integer 'Number of Fields
Dim Fd() As New Field 'Array of fields
Dim nCurField As Integer 'Counter for current field
Dim sTemp As String
On Error GoTo CRTError:
nFields = CInt(sGetINIString(sINIPath, sINISection, "Fields", "0"))
If nFields = 0 Then Exit Sub
ReDim Fd(1 To nFields)
tbl.Name = sTableName
For nCurField = 1 To nFields
Fd(nCurField).Name = sGetINIString_
(sINIPath, sINISection, "Fd" & nCurField & "Name", "ERROR" & _
[ccc] nCurField)
sTemp = sGetINIString(sINIPath, sINISection, "Fd" & nCurField & "Type", _
[ccc] "TEXT")
Select Case sTemp
Case "DOUBLE"
Fd(nCurField).Type = dbDouble
Case "MEMO"
Fd(nCurField).Type = dbMemo
'VB4/5 only
Fd(nCurField).AllowZeroLength = True
Case "BYTE"
Fd(nCurField).Type = dbByte
Case "INTEGER"
Fd(nCurField).Type = dbInteger
Case "DATE"
Fd(nCurField).Type = dbDate
Fd(nCurField).Required = False
Case Else 'Text
Fd(nCurField).Type = dbText
Fd(nCurField).Size = CInt(sGetINIString_
(sINIPath, sINISection, "Fd" & nCurField & "Size", "50"))
Fd(nCurField).AllowZeroLength = True
End Select
tbl.Fields.Append Fd(nCurField)
Next nCurField
Exit Sub
CRTError:
WriteErrMsg "CRT-Error " & Err & ": " & Error
End
Exit Sub
End Sub
Sub CreateLocalFile()
'This procedure creates the MDB file itself
Dim MainTable() As New TableDef
Dim sTemp As String
Dim nTables As Integer
Dim nCurTable As Integer
Dim sSQLTable As String
Dim sMDBTable As String
Dim sSection As String
On Error GoTo CRLError
If bFileExists(sDBLocalPath) Then Kill sDBLocalPath
Set dbLocal = CreateDatabase(sDBLocalPath, dbLangGeneral)
nTables = CInt(sGetINIString(sINIPath, "Tables", "Tables", "0"))
ReDim MainTable(1 To nTables)
For nCurTable = 1 To nTables
sSQLTable = sGetINIString(sINIPath, "tables", "table" & nCurTable & _
[ccc] "SQL", "none")
sMDBTable = sGetINIString(sINIPath, "tables", "table" & nCurTable & _
[ccc] "MDB", "none")
sSection = sGetINIString(sINIPath, "tables", "table" & nCurTable & _
[ccc] "INI", "none")
CreateTable MainTable(nCurTable), sMDBTable, sSection
dbLocal.TableDefs.Append MainTable(nCurTable)
Next nCurTable
Exit Sub
CRLError:
WriteErrMsg "CRL-Error " & Err & ": " & Error
End
Exit Sub
End Sub
Private Sub WriteErrMsg(sMessage As String)
'Should an error occur, this function writes it to
'another INI file. I did it this way because the
'program runs as a scheduled process on a remote
'machine, so no one would be there to answer an error
'dialog. There is a second VB program that continuously
'checks the Error.ini file and pages me with the error message.
Dim sErrorINI As String
sErrorINI = sGetINIString(sINIPath, "General", "ErrorINI", "error.ini")
writeINIString sErrorINI, "Error", "Message", sMessage
writeINIString sErrorINI, "Error", "Error", "True"
End Sub
First, the CreateLocalFile function gets the filename from the Dbpath= INI entry and uses Visual Basic's CreateDatabase function to create the new (and empty MDB) file. Next, the program uses a For loop to read through each table in the [Tables] section, repeatedly calling the CreateTable procedure. The CreateTable procedure, in turn, loops through the fields in the [tablename] section of the INI file, creating fields in the new table.
After a table is created, the TransferTable procedure takes care of transferring the data from an SQL Server table to one of the new tables. The procedure first creates a recordset from the SQL Server table and then loops through each record in the recordset, transferring the value for each field to the new table. During this process, users see a progress bar, as shown in Figure 23.4, to let them know something is happening.
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The SQL data export program displays a progress bar while in action.