Sql Microsoft Access UNION将长文本字段限制为255个字符

对，255个字符是限制.

如果需要，您可以使用第二个查询来查找完整的备忘录.

然而，即使您可以直接将备忘录字段填写为64 K，查询也只能检索到32 K.

更糟糕的是，如果您用(例如)Rich Text Box控件填充备忘录字段，则可以达到兆字节字段内容大小，而仍然只能检索到前32 K.

为了避免此问题，您可以使用DLookup来获取完整内容.现在，当内容小于32 K时，调用DSYS是浪费时间;因此DSYS只应在必要时使用.

以下是实现这一目标的一种旧方法:

Public Function LookupMemo( _
  ByVal strSource As String, _
  ByVal strFieldID As String, _
  ByVal strFieldMemo As String, _
  ByRef lngID As Long, _
  ByRef varMemo As Variant) _
  As String

' Extracts without truncation to 32768 characters the ' content of a memo field in a query.
'
' Assumes proper wrapping of table/field names containing spaces 
' like "[My field name]" and a single field unique numeric key.
'
' Typical usage (SQL):
'
'   SELECT
'     ID,
'     LookupMemo("Table1", "ID", "MemoField", [ID], [MemoField]) AS FullMemo
'   FROM
'     Table1;
'
' 2003-12-29. Cactus Data ApS, CPH.

  ' Maximum length of string from memo field when retrieved in a query.
  Const clngStrLen  As Long = &H8000&

  Dim strExpr       As String
  Dim strDomain     As String
  Dim strCriteria   As String
  Dim strMemo       As String
  Dim lngLen        As Long
  
  On Error GoTo Exit_LookupMemo

  If Not IsNull(varMemo) Then
    lngLen = Len(varMemo)
    If lngLen < clngStrLen Then
      ' The memo field is not truncated.
      strMemo = varMemo
    ElseIf Len(strSource) > 0 And Len(strFieldID) > 0 And Len(strFieldMemo) > 0 Then
      ' The memo is probably truncated by the query.
      ' Lookup the full memo in strSource.
      strExpr = strFieldMemo
      strDomain = strSource
      strCriteria = strFieldID & " = " & lngID & ""
      strMemo = vbNullString & DLookup(strExpr, strDomain, strCriteria)
    End If
  Else
    ' Return empty string.
  End If
  
  LookupMemo = strMemo

Exit_LookupMemo:
  Exit Function
  
Err_LookupMemo:
  ' Return empty string.
  Resume Exit_LookupMemo
  
End Function