Friday, September 28, 2012

Recreate Access Tables in SQL Server

by Roger Carlson


Microsoft Access is a terrific prototyping tool for SQL Server. But upsizing your database structure to a SQL Server database can be a problem. It would be nice if you could simply export the table structure from Access to SQL Server like you can between Access databases, but you can't. Fortunately, it's fairly easy to read the table structure of an Access table and from that build a SQL Create Table script to recreate the table in SQL Server.

Problems with the Access Upsize Wizard

Of course, Access comes with the Upsizing Wizard, which attempts to recreate your Access table in SQL Server. But the Upsizing Wizard has its problems.

First of all, the Upsize Wizard doesn't give you much flexibility. It chooses the SQL Server data types for your table. You don't have a choice. For instance, the wizard will create your text fields as nvarchar, but suppose you want them created as varchar? What if you want your Yes/No fields created as tinyint rather than bit?

And then there are SQL Server specific properties, like Padding and Clustered Indexes, over which you have no control. The Upsizing Wizard will apply a default padding value, which you cannot change. It will also always create your primary key as a clustered index, whether you want it or not.

Another problem with the Upsize Wizard is you must be connected to a SQL Server database for it to work. This is fine if you have a connection, but suppose you don't have rights to create tables? What if the SQL Server DBA asks you for a script to create them? What if you need to send the table definitions to a remote location to be created there?

Lastly, the Upsize Wizard will only work with SQL Server. The following process could be easily modified to create your tables in Oracle or another SQL-based database.

SQL Server's Enterprise Manager has a function that will save the structure of a table as a Create Table statement in a text file. Your DBA can then to run this script in the Query Analyzer to create the tables for you. It would be really useful if Access had a similar facility, but it does not. Fortunately, you can write one of your own.

How it works

The following code module accepts the name of a table in your Access database. It will then read the field names and data types and build a SQL Create Table statement, converting the Access data types to SQL Server equivalent data types. It then writes this SQL statement to a text file named after the table and having a .SQL extension.

Next, it reads all the Indexes in the table, determines the fields in the index and whether it is Unique or a Primary Key index, and finally builds Create Index statements to recreate these indexes.

Public Sub RecreateTableInSQLServer(TableName As String)
On Error GoTo Err_RecreateTableInSQLServer

The first thing is to create some object and scalar variables.

Dim dbs As DAO.Database, tdf As DAO.TableDef
Dim fld As DAO.Field, idx As DAO.Index
Dim strSQL As String
Dim indexfields As String
Dim indexunique As String
Dim path As String

Next, you need to initialize the object variables, opening a connection to the current database and to the particular table you want to recreate.

Set dbs = CurrentDb
Set tdf = dbs.TableDefs(TableName)

You also want to find the path to the folder where the database currently resides, so the program will know where to store the text file.

path = (Mid(dbs.Name, 1, Len(dbs.Name) - Len(Dir(dbs.Name))))

If you want some other directory, you could hard code a folder path here.

path = "C:\My Documents\Access"

In Access, any field can be defined as part of a primary key as long as there aren't any null values in the field. In SQL Server, however, you must define the field as Not Null ahead of time. Therefore, you have to know which fields are in the primary key before you start defining the fields. To do that, you have to loop through the Indexes collection of the TableDef object. When you find the primary key index (as determined by the Primary property of the Index object), assign it to a string variable (indexfields).

For Each idx In tdf.Indexes
    If idx.Primary = True Then
    indexfields = idx.Fields
    End If

The fields that make up the index are stored in the Fields property of the Index object, but they are stored in an odd format. For a multiple field index, they're stored in a string that looks something like this: +TextField;+LongIntField. Fortunately, you can read this string for the fieldnames with the InStr() function. You'll do this later in the routine.

Now that all the variables are created and initialized, and you know what fields are in the primary key, you can begin to build the SQL statement. Every Create Table statement always starts with the word CREATE TABLE and the name of the table. So you'll write that to a string variable (strSQL).

strSQL = "CREATE TABLE [" & TableName & "] ("

The brackets surrounding both the table name above and the field names below are necessary for table and field names that have spaces or special characters in them.

Next, the code needs to read through all the fields in the table, read the data types, and in some cases, determine some field attributes. It will add the field to the field list of the Create Table statement and depending on the data type, add the corresponding SQL Server data type.

For Each fld In tdf.Fields
  Select Case fld.Type
    Case 4 'Long Integer or Autonumber field
      If fld.Attributes = 17 Then
        strSQL = strSQL & "[" & fld.Name & "] INT IDENTITY"
        strSQL = strSQL & "[" & fld.Name & "] INT"
      End If
    Case 10 'Text field
       strSQL = strSQL & "[" & fld.Name & "] VARCHAR(" & fld.Size & ")"
    Case 12 'Memo field
strSQL = strSQL & "[" & fld.Name & "] NTEXT"
    Case 2 'Byte field
       strSQL = strSQL & "[" & fld.Name & "] SMALLINT"
    Case 3 'Integer field
       strSQL = strSQL & "[" & fld.Name & "] SMALLINT"
    Case 6 'Single-precision field
       strSQL = strSQL & "[" & fld.Name & "] REAL"
    Case 7 'Double-precision field
       strSQL = strSQL & "[" & fld.Name & "] FLOAT"
    Case 15 'ReplicationID field
       strSQL = strSQL & "[" & fld.Name & "] UNIQUEIDENTIFIER"
    Case 8 'Date/Time field
       strSQL = strSQL & "[" & fld.Name & "] DATETIME"
    Case 5 'Currency field
       strSQL = strSQL & "[" & fld.Name & "] MONEY"
    Case 1 'Yes/No field
       strSQL = strSQL & "[" & fld.Name & "] SMALLINT"
    Case 11 'OleObject field
       strSQL = strSQL & "[" & fld.Name & "] IMAGE"
  End Select

This is where you'll use the index string of the primary key. If the field is part of the primary key, add NOT NULL to the field data type, otherwise just append a comma.

  If InStr(indexfields, fld.Name) > 0 Then
    strSQL = strSQL & " NOT NULL, "
    strSQL = strSQL & ", "
  End If

And go to the next field.

Next fld

There will be an extra comma at the end the field list that needs to be removed. You also have to close off the Create Table statement with a closing paren and semicolon. (Technically, the semi-colon is unnecessary).

strSQL = Left(strSQL, Len(strSQL) - 2) & ");"

Now, you need to create a text file and write the string variable to that file. The easiest way to do this is through low-level IO. The following Open statement will create a text file with the name of the table preceded by the word "Create" and followed with a .sql extension in the folder where the database resides. So for table "Customers", the text file would be "CreateCustomers.sql". Then it will use the Print command to write the SQL statement to the file followed by a blank line.

Open path & "Create" & TableName & ".sql" For Output As #1
Print #1, strSQL
Print #1, ""

Next you need to recreate the indexes themselves, so you need to read the indexes again.

For Each idx In tdf.Indexes

As I said earlier, the index property returns a string like this: +TextField;+LongIntField. To make it useful for a SQL statement, you need to remove the pluses and convert the semicolons to commas. This you can do with the Replace function.

  indexfields = idx.Fields
  indexfields = Replace(indexfields, "+", "")
  indexfields = Replace(indexfields, ";", "], [")

In the first Replace function, you will replace all the pluses with the empty string, effectively deleting them. In the second Replace function, you are replacing each semicolon with "], [". The brackets are necessary for field names that have spaces in them. The first and last fields in the field list will not have brackets on the outer edge, but we'll add them when we put the whole SQL statement together.

You also need to determine whether the index is unique. If it is, the Unique property of the Index object will be true.

  If idx.Unique = True Then
    indexunique = " UNIQUE "
    indexunique = ""
  End If

You are almost ready to put the SQL Statement together. There is just one more property you need to consider whether the index is a primary key. In Access, you can create the Primary Key index in the Create Index statement. However, in SQL Server, you have to create it in the Create Table or Alter Table statement. I've chosen to do it in the Alter Table statement.

So if the index is a primary key index, use the Alter Table statement to create the primary key. Otherwise, build a Create Index statement.

  If idx.Primary = True Then
    strSQL = "ALTER TABLE [" & TableName & _
    "] ADD CONSTRAINT [PK_" & TableName & "_" & idx.Name & _
    "] PRIMARY KEY ([" & indexfields & "]);"
    strSQL = "CREATE " & indexunique & _
    " INDEX [IX_" & TableName & "_" & idx.Name & _
    "] On [" & TableName & "] ([" & indexfields & "]);"
  End If

Since your text file is still open, you can simply write the SQL string to it. Then loop for the next index.

  Print #1, strSQL
  Print #1, ""

When you're done reading the indexes, close the text file and destroy the object variables.

Close #1
Set idx = Nothing
Set tdf = Nothing
Set dbs = Nothing

Add error trapping, and you're done.

Exit Sub
MsgBox Err.Description
   Resume Exit_RecreateTableInSQLServer
End Sub

Implementing the Routine

Implementing this routine is relatively easy. Create a form with a listbox and a button. Fill the listbox (we'll call it lstTableList) with all the tables in your database by putting the following in the RowSource property of your listbox:

SELECT MSysObjects.Name, MSysObjects.Type
FROM MSysObjects
WHERE (((MSysObjects.Name) Not Like "msys*"
  And (MSysObjects.Name) Not Like "~*")
  AND ((MSysObjects.Type)=1))
  ORDER BY MSysObjects.Name;

Then call the routine from the button like this:

Call RecreateTableInSQLServer(Me.lstTableList)


Figure 1: Form used to implement the RecreateTableInSQLServer routine

The resulting text file might look like this:

CREATE TABLE [tblAllDataTypes] ([AutoNumberField] INT IDENTITY NOT NULL,
[TextField] VARCHAR(50) NOT NULL, [MemoField] NTEXT, [LongIntField] INT, [ByteField] SMALLINT, [IntegerField] SMALLINT, [SingleField] REAL, [DoubleField] FLOAT, [ReplicationField] UNIQUEIDENTIFIER, [DateTimeField] DATETIME, [CurrencyField] MONEY, [YesNoField] SMALLINT, [OLEObjectField] IMAGE, [HyperLinkField] NTEXT);

CREATE INDEX [IX_tblAllDataTypes_Index1] On [tblAllDataTypes] ([TextField], [LongIntField]);

CREATE UNIQUE INDEX [IX_tblAllDataTypes_LongIntField] On [tblAllDataTypes] ([LongIntField]);

ALTER TABLE [tblAllDataTypes] ADD CONSTRAINT [PK_tblAllDataTypes_PrimaryKey] PRIMARY KEY ([AutoNumberField], [TextField]);

Considerations for Access Versions

This routine requires a reference set to the DAO (Data Access Objects) object model. This is not a problem in Access 97, 2003 or 2007, but in Access 2000 and 2002 (XP), you'll have to set this reference.

To do that, go to the VB editor (Alt+F11), and from the menu bar select Tools > References. In the References dialog box, scroll down the list until you find Microsoft DAO 3.6 Object Library. Check the box next to it and click OK to close the box.

Access 97 has an additional problem. The Replace function used above does not exist in Access 97, so you'll need to create one. Fortunately, it's relatively simple.

Function ReplaceCharacter(Target As String, SearchChar, ReplaceChar) As String

Dim i As Integer
Dim tempstring As String
  For i = 1 To Len(Target)
    If Mid(Target, i, 1) = SearchChar Then
      tempstring = tempstring & ReplaceChar
      tempstring = tempstring & Mid(Target, i, 1)
    End If
  Next i
ReplaceCharacter = tempstring
End Function

To use this function, simply replace these lines:

indexfields = Replace(indexfields, "+", "")
indexfields = Replace(indexfields, ";", "], [")

with these:

indexfields = ReplaceCharacter (indexfields, "+", "")
indexfields = ReplaceCharacter (indexfields, ";", "], [")


There are a variety of circumstances where you might want to recreate an Access table in other database environments. This routine demonstrates a fairly simple method to save the table structure complete with indexes into a SQL script file that can be run in the target environment to recreate the table.

Sample Database

You can find a sample which implements this here:

1 comment:

TCoal said...

Nice fix. I'm new to Access and this is a bit beyond me but it's good to know there's solutions if I ever encounter this.