机房收费系统之组合查询

对于机房收费系统，总体来说不太难，比较让人费脑筋的地方也不过上下机，组合查询和结账部分，这三部分是需要我们动脑筋的，在做之前，我们得先熟悉这几部分的作用是什么，它们能实现什么功能，只有我们把其中的逻辑思路理清了，在接下来实际操作完善的时候才会得心应手。组合查询的实现有很多种方式，各有优劣，下面是我实现组合查询的部分代码。以学生上机统计信息窗体为例。

从左到右各个控件的名称为：cboField(0)，cboOperator(0)，Text1(0)，DTP1，cboRelation(0)

cboField(1)，cboOperator(1)，Text1(1)，DTP2，cboRelation(1)

cboField(2)，cboOperator(2)，Text1(2)，DTP3，cboRelation(2)

Form_Load()中添加combobox的加载信息和设置第二和第三行的查询条件不可用

   Dim a, b, c 
    For a = 0 To 2
        With cboField(a)
            .AddItem ""
            .AddItem "卡号"
            .AddItem "姓名"
            .AddItem "上机日期"
            .AddItem "上机时间"
            .AddItem "下机日期"
            .AddItem "下机时间"
            .AddItem "消费金额"
            .AddItem "余额"
        End With
    Next a
    For b = 0 To 2
        With cboOperator(b)
            .AddItem ""
            .AddItem "="
            .AddItem "<>"
            .AddItem "<"
            .AddItem ">"
         End With
    Next b
    For c = 0 To 1
         With cboRelation(c)
              .AddItem ""
              .AddItem "与"
              .AddItem "或"
         End With
    Next c

    cboField(1).Enabled = False
    cboOperator(1).Enabled = False
    Text1(1).Enabled = False
    cboField(2).Enabled = False
    cboOperator(2).Enabled = False
    Text1(2).Enabled = False
    cboRelation(1).Enabled = False

然后定义了一个过程，保证可以从数据库中选择正确的字段

Public Function Fieldname(strFiledname As String) As String

 Select Case strFiledname
    Case "卡号"
       Fieldname = "cardno"
    Case "姓名"
       Fieldname = "studentName"
    Case "上机日期"
       Fieldname = "ondate"
    Case "上机时间"
       Fieldname = "ontime"
    Case "下机日期"
       Fieldname = "offdate"
    Case "下机时间"
       Fieldname = "offtime"
    Case "消费金额"
       Fieldname = "consume"
    Case "余额"
       Fieldname = "cash"

  End Select

End Function

然后就是字段名的click事件，添加了DTP控件选择日期和时间，可以避免输入错误的时间格式。

Private Sub cboField_Click(Index As Integer)
 If Trim(cboField(0).Text) = "上机日期" Or Trim(cboField(0).Text = "下机日期") Then
        DTP1.Visible = True


        ElseIf Trim(cboField(0).Text) = "上机时间" Or Trim(cboField(0).Text) = "下机时间" Then
        DTP1.Visible = True
        DTP2.Visible = False
        DTP3.Visible = False
        DTP1.Format = dtpTime
        DTP1.Value = Time
     End If

     If Trim(cboField(1).Text) = "上机日期" Or Trim(cboField(1).Text = "下机日期") Then
        DTP2.Visible = True


      ElseIf Trim(cboField(1).Text) = "上机时间" Or Trim(cboField(1).Text) = "下机时间" Then
        DTP2.Visible = True
        DTP1.Visible = False
        DTP3.Visible = False
        DTP2.Format = dtpTime
        DTP2.Value = Time
     End If

     If Trim(cboField(2).Text) = "上机日期" Or Trim(cboField(2).Text = "下机日期") Then
        DTP3.Visible = True

      ElseIf Trim(cboField(2).Text) = "上机时间" Or Trim(cboField(2).Text) = "下机时间" Then
        DTP3.Visible = True
        DTP1.Visible = False
        DTP2.Visible = False
        DTP3.Format = dtpTime
        DTP3.Value = Time
     End If

End Sub

判断第一个和第二个的选择关系，有还是没有“与” 或 “或”

Private Sub cboRelation_Click(Index As Integer)
If Trim(cboRelation(0).Text) <> "" Then '第一个关系不为空时，第二行可用
cboField(1).Enabled = True
cboOperator(1).Enabled = True
Text1(1).Enabled = True
cboRelation(1).Enabled = True
End If

If Trim(cboRelation(1).Text) <> "" Then '第一个关系不为空时，第二行可用
cboField(2).Enabled = True
cboOperator(2).Enabled = True
Text1(2).Enabled = True

End If
End Sub

接下来就是查询按钮里的东西了

If Trim(cboField(0).Text) = "" Or Trim(cboOperator(0).Text) = "" Or Trim(Text1(0).Text) = "" Then
MsgBox "请把您的输入项填写完整", vbOKOnly + vbExclamation, "警告！"
Exit Sub
Else
txtsql = "select * from line_info where " & Fieldname(cboField(0).Text) & cboOperator(0).Text & "'" & Text1(0).Text & "'"
Set mrc = ExecuteSQL(txtsql, msgtext)
从数据库中选择信息就采用了上面的办法，当条件多的时候方法类似，

接下来就是理清选择关系，当第一个选择关系不为空时，当第二个选择关系不为空时

然后就是通过DTP控件的选择和失去焦点来让DTP控件给文本框赋值，

Private Sub DTP1_Change()
    Text1(0).Text = DTP1.Value

End Sub
Private Sub DTP2_Change()
    Text1(1).Text = DTP2.Value

End Sub
Private Sub DTP3_Change()
    Text1(2).Text = DTP3.Value

End Sub

Private Sub DTP1_LostFocus()
    Text1(0).Text = DTP1.Value
    DTP1.Visible = False
End Sub
Private Sub DTP2_LostFocus()
    Text1(1).Text = DTP2.Value
    DTP2.Visible = False
End Sub
Private Sub DTP3_LostFocus()
    Text1(2).Text = DTP3.Value
    DTP3.Visible = False
End Sub

这样就会在选择到日期或时间条件时通过DTP控件来得到便利。还有这里用到了数组，可谓是给清空时节省了一大部分代码，这一部分难的是理清选择条件，好好思考下选择条件就会发现也不过如此。

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机房收费系统之组合查询

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