机房收费系统---------组合查询

终于算是接触到机房里的重点加难点里的组合查询了，这个知识点说简单也简单，说难也难，关键是对他的理解到了哪一步。

什么是组合查询

大多数的SQL查询只包含从一个或多个表中返回数据的单条SELECT语句，但是,SQL也允许执行多个查询(多条SELECT语句),并将结果作为一个查询结果集返回。这些组合查询通常称为并或复合查询。

主要有两种情况需要使用组合查询：

(1)在一个查询中从不同的表返回结构数据

(2)对一个执行多个查询，按一个查询返回数据

首先是组合框列表的字段转换

    Select Case Trim(comboField)
        Case "卡号"
            FileName = "cardno"
        Case "姓名"
            FileName = "studentname"
        Case "上机日期"
            FileName = "ondate"
        Case "上机时间"
            FileName = "ontime"
        Case "下机日期"
            FileName = "offdate"
        Case "下机时间"
            FileName = "offtime"
        Case "消费金额"
            FileName = "consume"
        Case "金额"
            FileName = "cash"
        Case "备注"
            FileName = "status"
    End Select
End Function

还有就是要根据不同的内容选用不同的操作符

If combol(Index).Text = "姓名" Then
        Symbol(Index).Clear
        Symbol(Index).AddItem "="
        Symbol(Index).AddItem "<>"
    Else
        Symbol(Index).Clear
        Symbol(Index).AddItem "="
        Symbol(Index).AddItem ">"
        Symbol(Index).AddItem "<"
        Symbol(Index).AddItem "<>"
    
    End If

接下来就是组合关系

   
'第一组判断
 '如果第一个字段名为空或者第一个操作符为空或内容为空，则显示msgbox中的内容，否则，退出程序
    If Trim(comboField1.Text) = "" Or Trim(comboOpsign1.Text) = "" Or Trim(txtContent1.Text) = "" Then
        MsgBox "请将第一行内容填写完整", 0, "温馨提示"
        Exit Sub
    Else
    '将查询到的部分赋予到combo框中
    txtsql = txtsql & " " & field(comboField1.Text) & " " & Trim(comboOpsign1.Text) & "'" & Trim(txtContent1.Text) & "'"
    '第二组判断
        If comboRelation1.Text <> "" Then
        Select Case Trim(comboField2.Text)
    '判断是否为日期型
    Case "上机日期"
        DTPicker2.MaxDate = Date
        If Format(DTPicker2.Value, "yyyy-mm-dd") > Format(DTPicker2.MaxDate, "yyyy-mm-dd") Then
            MsgBox "您选择的日期不能大于当前日期", 0 + 48, "提示"
            Exit Sub
        End If
            txtContent2.Text = Format(DTPicker2.Value, "yyyy-mm-dd")
        Case "下机日期"
            DTPicker2.MaxDate = Date
            If Format(DTPicker2.Value, "yyyy-mm-dd") > Format(DTPicker2.MaxDate, "yyyy-mm-dd") Then
                MsgBox "您选择的日期不能大于当前日期", 0 + 48, "提示"
                Exit Sub
            End If
            txtContent2.Text = Format(DTPicker2.Value, "yyyy-mm-dd")
            '判断是否为时间类型
            Case "上机时间"
                txtContent2.Text = Format(DTPicker2.Value, "hh:mm:ss")
            Case "下机时间"
                txtContent2.Text = Format(DTPicker2.Value, "hh:mm:ss")
            '为其他
            If Trim(txtContent2.Text) = "" Then
                txtContent2.SetFocus
            End If
        End Select
            If Trim(comboField2.Text) = "" Or Trim(comboOpsign2.Text) = "" Or Trim(txtContent2.Text) = "" Then
                MsgBox "请将第二行内容填写完整", 0, "温馨提示"
                Exit Sub
            Else
                txtsql = txtsql & " " & RelationName(comboRelation1.Text) & " " & field(comboField2.Text) & " " & comboOpsign2.Text & "'" & Trim(txtContent2.Text) & "'"

        '第三组判断
            If comboRelation2.Text <> "" Then
            Select Case Trim(comboField3.Text)
    '判断是否为日期型
    Case "上机日期"
        DTPicker3.MaxDate = Date
        If Format(DTPicker3.Value, "yyyy-mm-dd") > Format(DTPicker3.MaxDate, "yyyy-mm-dd") Then
            MsgBox "您选择的日期不能大于当前日期", 0 + 48, "提示"
            Exit Sub
        End If
            txtContent3.Text = Format(DTPicker3.Value, "yyyy-mm-dd")
        Case "下机日期"
            DTPicker3.MaxDate = Date
            If Format(DTPicker3.Value, "yyyy-mm-dd") > Format(DTPicker3.MaxDate, "yyyy-mm-dd") Then
                MsgBox "您选择的日期不能大于当前日期", 0 + 48, "提示"
                Exit Sub
            End If
            
            txtContent3.Text = Format(DTPicker3.Value, "yyyy-mm-dd")
            
            '判断是否为时间类型
            Case "上机时间"
                
                txtContent3.Text = Format(DTPicker3.Value, "hh:mm:ss")
            Case "下机时间"
                txtContent3.Text = Format(DTPicker3.Value, "hh:mm:ss")
            '为其他
            If Trim(txtContent3.Text) = "" Then
                txtContent3.SetFocus
            End If
        End Select
                If Trim(comboField3.Text) = "" Or Trim(comboOpsign3.Text) = "" Or Trim(txtContent3.Text) = "" Then
                    MsgBox "请将第三行内容填写完整", 0, "温馨提示"
                    Exit Sub
                Else
                    txtsql = txtsql & " " & RelationName(comboRelation2.Text) & " " & field(comboField3.Text) & " " & comboOpsign3.Text & "'" & Trim(txtContent3.Text) & "'"
                    
                End If
            End If
         End If
      End If 
   End If
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