使用VBA向MS Access表添加字段

Question

我需要将计算字段添加到现有表中。我知道有两种方法可以做到这一点，并且我想知道是否有人对最好的方法以及如何使它们起作用具有任何投入：

1. 使用TableDef.CreateField，然后使用TableDef.Fields.Append
2. 使用DDL Alter Table ADD COLUMN语句

我尝试使用第一种方法，但是由于Access无法锁定表，因此我一直收到3211错误。我没有打开桌子。但是，我从已访问表中当前存在哪些字段的窗体调用CreateField。

这是调用CreateField的代码：

`
Public Sub AddFieldToTable(strTable As String, strField As String, nFieldType As     Integer)

    Dim db As DAO.Database
    Dim tdf As DAO.TableDef
    Dim fld As DAO.Field

    On Error GoTo ErrorHandler

    Set db = CurrentDb
    Set tdf = db.TableDefs(strTable)
    Set fld = tdf.CreateField(strField, nFieldType)
    tdf.Fields.Append fld

    MsgBox "The field named [" & strField & "] has been added to table [" & strTable & "]."

    Set tdf = Nothing
    Set db = Nothing

    Exit Sub

    ErrorHandler:
        MsgBox "An error has occurred. Number: " & Err.Number & ", description: " &        Err.Description
        Exit Sub

End Sub
`

我在tdf.fields.append行上收到错误。执行ALTER TABLE语句会更好吗？有哪些权衡？

Answer 1

您可以使用DDL创建字段：

长：

CurrentDb.Execute "ALTER TABLE t ADD COLUMN a Long not null", dbFailOnError 

（NOT NULL IDENTITY(1,1)争取自动编号）

CurrentDb.Execute "ALTER TABLE t ADD COLUMN b text(100)", dbFailOnError 

布尔值：

CurrentDb.Execute "ALTER TABLE t ADD COLUMN c Bit not null", dbFailOnError 

约会时间：

CurrentDb.Execute "ALTER TABLE t ADD COLUMN d datetime null", dbFailOnError 

备忘录：

CurrentDb.Execute "ALTER TABLE t ADD COLUMN e memo null", dbFailOnError 

显然，这很适合进行功能化，您可以传入自己的永恒枚举（与结合使用Select）来构造字符串并执行它：

Public Sub AddFieldToTable(TableName as string, FieldName as string, _
      FieldType as Long, FieldLen as Long, FieldAllowsNull as Boolean)

Dim FieldText as String

Select Case(FieldType)
    Case 0:
        FieldText = "Long"
    Case 1:
        FieldText = "text(" & FieldLen & ")"
    Case 2:
        FieldText = "bit"
    Case 3:
        FieldText = "datetime"
    Case 4:
        FieldText = "memo"

End Select

Dim Sql as string
Sql = "ALTER TABLE " & TableName & " ADD COLUMN " & FieldName & " " & FieldText

If FieldAllowsNull then
   Sql = Sql & " NULL"
Else
   Sql = Sql & " NOT NULL"
End If

CurrentDb.Execute Sql, dbFailOnError

End Sub