机房收费系统——组合查询

大家好，又见面了，我是你们的朋友全栈君。组合查询也是我们在机房收费系统中接触到的一个新东西，一开始无从下手，后来也在摸爬滚打中实现了。首先思路要清晰，明白这些功能的内在逻辑关系，代码实现起来才会更顺畅。

就拿操作员工作记录窗体来说，

一.判断第1行查询条件是否为空，若都不为空而且组合关系4 为空，查询到的结果符合第一行查询条件。

二.若组合关系4 为“与” 或 “或”，且组合关系5 为空，则第二行查询条件都不能为空，查询到的结果符合第一行和第二行查询条件组合后查询到的内容。

三.若组合关系4和5都不为空，三行查询条件都得填好，则查询到的是三行共同组合后的内容。

如果4为空，则2,3,5中控件的enabled属性为False，如果不为空，将激活2,5中控件的enabled属性为True。

’现在发现自己敲的时候没注意明明规范，大家可能看不太懂
'combo1:字段名
'combo2:操作符
'combo3：组合关系


Private Sub Form_Load()
    Dim i, j, k
    Me.Height = 10185
    Me.Width = 15135

    '加载窗体时依次填充comboBox的下拉列表
    For i = 0 To 2
        With Combo1(i)
            .AddItem "教师"
            .AddItem "注册时间"
            .AddItem "注册日期"
            .AddItem "注销时间"
            .AddItem "注销日期"
            .AddItem "机器名"
        End With
    Next i
    
    For j = 0 To 2
        With Combo2(j)
            .AddItem "="
            .AddItem "<"
            .AddItem ">"
            .AddItem "<>"
        End With
    Next j
    
    For k = 0 To 1
        With Combo3(k)
            .AddItem "与"
            .AddItem "或"
        End With
    Next k

  ’如果组合查询框为空（不是“与”也不是“或”），不能添加下面的查询条件
   If Combo3(0).Text = Trim("") Then
        Combo1(1).Enabled = False
        Combo1(2).Enabled = False
        Combo2(1).Enabled = False
        Combo2(2).Enabled = False
        Text2.Enabled = False
        Text3.Enabled = False
        Combo3(1).Enabled = False
    End If
    
    If Combo3(1).Text = Trim("") Then
        Combo1(2).Enabled = False
        Combo2(2).Enabled = False
        Text3.Enabled = False
    End If  
End Sub


'激活
Private Sub Combo3_Click(Index As Integer)
    If Combo3(0).Text <> Trim("") Then
        Combo1(1).Enabled = True
        Combo2(1).Enabled = True
        Combo3(1).Enabled = True
        Text2.Enabled = True
    End If
    
    If Combo3(1).Text <> Trim("") Then
        Combo1(2).Enabled = True
        Combo2(2).Enabled = True
        Text3.Enabled = True
    End If
    
End Sub


Private Sub cmdInquire_Click()
    Dim MsgText As String
    Dim txtSQL As String
    Dim mrc As ADODB.Recordset
    Dim strCon1, strCon2, strcon3, strcon4, strcon5
  
’把汉字转换成数据库中的字段名，实现第一行查询  
    Select Case Combo1(0).Text
        Case "教师"
            strCon1 = " UserID"
        Case "注册时间"
            strCon1 = " LoginTime"
        Case "注册日期"
            strCon1 = " LoginDate"
        Case "注销时间"
            strCon1 = "LogoutTime"
        Case "注销日期"
            strCon1 = "logoutDate"
        Case "机器名"
            strCon1 = " Computer"
    End Select
    
    If Not Testtxt(Combo1(0).Text) Then
        MsgBox "请选择字段名", vbOKOnly + vbExclamation, "提示"
        Combo1(0).SetFocus
        Exit Sub
    ElseIf Not Testtxt(Combo2(0).Text) Then
        MsgBox "请选择操作符", vbOKOnly + vbExclamation, "提示"
        Combo2(0).SetFocus
        Exit Sub
    ElseIf Not Testtxt(Text1.Text) Then
        MsgBox "请输入要查询的内容"
        Text1.SetFocus
        Exit Sub
    Else
        txtSQL = "select * from worklog_Info where " & strCon1 & Combo2(0).Text & "'" & Text1.Text & "'"
        Set mrc = ExecuteSQL(txtSQL, MsgText)
        
        If mrc.EOF Then
            MsgBox "该条件的数据不存在", vbOKOnly + vbExclamation, "提示"
            Exit Sub
        End If
    End If
 
'实现第二行查询   
    If Not Testtxt(Combo3(0).Text) Then
        GoTo Case1
    Else
        Select Case Combo3(0).Text
            Case "与"
                strCon2 = "and"
            Case "或"
                strCon2 = "or"
        End Select
                
        Select Case Combo1(1).Text
            Case "教师"
                strcon3 = "UserID"
            Case "注册时间"
                strcon3 = "LoginTime"
            Case "注册日期"
                strcon3 = "LoginDate"
            Case "注销时间"
                strcon3 = " LogoutTime"
            Case "注销日期"
                strcon3 = " logoutDate"
            Case "机器名"
                strcon3 = "Computer"
        End Select
        
        If Not Testtxt(Combo1(1).Text) Then
            MsgBox "请选择字段名", vbOKOnly + vbExclamation, "提示"
            Combo1(1).SetFocus
            Exit Sub
        ElseIf Not Testtxt(Combo2(1).Text) Then
            MsgBox "请选择操作符", vbOKOnly + vbExclamation, "提示"
            Combo2(1).SetFocus
            Exit Sub
        ElseIf Not Testtxt(Text2.Text) Then
            MsgBox "请输入要查询的内容", vbOKOnly + vbExclamation, "提示"
            Text2.SetFocus
            Exit Sub
        ElseIf Combo1(1).ListIndex = 1 Or 2 Or 3 Or 4 Then
            MonthView1.Visible = True
            Text2.Text = MonthView1.Value
        Else
            txtSQL = txtSQL & strCon2 & " " & strcon3 & Combo2(1).Text & "'" & Text2.Text & "'"
            Set mrc = ExecuteSQL(txtSQL, MsgText)
            
            If mrc.EOF Then
                MsgBox "该条件的数据不存在", vbOKOnly + vbExclamation, "提示"
                Exit Sub
            End If
        End If
    End If
    
’实现第三行查询
    If Trim(Combo3(1).Text) = "" Then
        GoTo Case1
    Else
        Select Case Combo3(1).Text
            Case "与"
                strcon4 = "and"
            Case "或"
                strcon4 = "or"
        End Select
        
        Select Case Combo1(2).Text
            Case "教师"
                strcon5 = "UserID"
            Case "注册时间"
                strcon5 = "LoginTime"
            Case "注册日期"
                strcon5 = "LoginDate"
            Case "注销时间"
                strcon5 = " LogoutTime"
            Case "注销日期"
                strcon5 = " logoutDate"
            Case "机器名"
                strcon5 = "Computer"
        End Select
    

        If Not Testtxt(Combo1(2).Text) Then
            MsgBox "请选择字段名", vbOKOnly + vbExclamation, "提示"
            Combo1(2).SetFocus
            Exit Sub
        End If
        
        If Not Testtxt(Combo2(2).Text) Then
            MsgBox "请选择操作符", vbOKOnly + vbExclamation, "提示"
            Combo2(2).SetFocus
            Exit Sub
        End If
        
        If Not Testtxt(Text3.Text) Then
            MsgBox "请输入要查询的内容", vbOKOnly + vbExclamation, "提示"
            Text3.SetFocus
            Exit Sub
        End If
        
        If Combo1(2).ListIndex = 1 Or 2 Or 3 Or 4 Then
            MonthView1.Visible = True
            Text3.Text = MonthView1.Value
        End If
        
        txtSQL = txtSQL & strcon4 & " " & strcon5 & Combo2(2) & "'" & Text3.Text & "'"
        Set mrc = ExecuteSQL(txtSQL, MsgText)
        
        If mrc.EOF Then
            MsgBox "该条件的数据不存在", vbOKOnly + vbExclamation, "提示"
            Exit Sub
        End If
    End If
        
    
Case1:
    With myflexgrid
        .Rows = 1
        .CellAlignment = 4
        .TextMatrix(0, 0) = "序列号"
        .TextMatrix(0, 1) = "教师"
        .TextMatrix(0, 2) = "级别"
        .TextMatrix(0, 3) = "注册日期"
        .TextMatrix(0, 4) = "注册时间"
        .TextMatrix(0, 5) = "注销日期"
        .TextMatrix(0, 6) = "注销时间"
        .TextMatrix(0, 7) = "机器名"
        .TextMatrix(0, 8) = "状态"
        
        Do While Not mrc.EOF
            .Rows = .Rows + 1
            .CellAlignment = 4
            .TextMatrix(.Rows - 1, 0) = Trim(mrc.Fields(0))
            .TextMatrix(.Rows - 1, 1) = Trim(mrc.Fields(1))
            .TextMatrix(.Rows - 1, 2) = Trim(mrc.Fields(2))
            .TextMatrix(.Rows - 1, 3) = Trim(mrc.Fields(3))
            .TextMatrix(.Rows - 1, 4) = Trim(mrc.Fields(4))
            .TextMatrix(.Rows - 1, 5) = Format(mrc.Fields(5))
            .TextMatrix(.Rows - 1, 6) = Format(mrc.Fields(6))
            .TextMatrix(.Rows - 1, 7) = Trim(mrc.Fields(7))
            .TextMatrix(.Rows - 1, 8) = Trim(mrc.Fields(8))
            mrc.MoveNext
        Loop
    End With  
End Sub

这么长的代码终于实现了组合查询的功能，但是大家可能发现在查询的过程中，有很多代码是重复的，有没有更好的方法呢？

优化1：

在代码中多次用到了把comboBox中下拉列表的汉字转换成连接数据库时可以识别的，与数据库字段一致的英文，这些代码多次重复，是不是会占用很多内存呢？我们可以自定义一个函数，解决这个问题。

Private Function FieldName(strFieldName as String) As String
        Select Case strFieldName
            Case "教师"
                FieldName = "UserID"
            Case "注册时间"
                FieldName = "LoginTime"
            Case "注册日期"
                FieldName = "LoginDate"
            Case "注销时间"
                FieldName = " LogoutTime"
            Case "注销日期"
                FieldName = " logoutDate"
            Case "机器名"
                FieldName = "Computer"
        End Select

End Sub

'以条件1和2组合为例，相应的连接数据库的代码可改为

Private Sub cmdInquire_Click()

	txtSQL="select * from worklog_Info where " & FieldName(combo1(0).Text) 
	       & combo2(0).Text & "'" & text1.Text & "'"
	Select Case combo3(0).Text
	     Case "或"
		txtSQL=txtSQL & "or" & FieldName(combo1(1).Text) 
			& combo2(1).Text & "'" & text2.Text & "'"
	     Case "与"
		txtSQL=txtSQL & "and" & FieldName(combo1(1).Text) 
			& combo2(1).Text & "'" & text2.Text & "'"
	End Select
End Sub
Private Function FieldName1(strFieldName as String)As String
	Select Case strFieldName
	      Case "与"
		  FieldName = "and"
	      Case "或"
		  FieldName = "or"
	End Select
End Sub
'或者也可以这么写
Private Sub cmdInquire_Click()
	txtSQL="select * from worklog_Info where "
	strA= FieldName(combo1(0).Text) & combo2(0).Text & "'" & text1.Text & "'"
	strB=FieldName1(combo3(0).Text) & FieldName(combo1(1).Text) & combo2(1).Text 
		& "'" & text2.Text & "'"
	strC=FieldName1(combo3(1).Text) & FieldName(combo1(2).Text) & combo2(2).Text 
		& "'" & text3.Text & "'"
	txtSQL=txtSQL & strA & strB & strC
End Sub

优化2：

在最初的代码中，也曾多次用到了判断查询条件是否为空的语句，看师哥师姐的博客，也可以用一个相应的函数来实现

Public Function Testtxt(txt As String) As Boolean
    If Trim(txt) = "" Then
        Testtxt = False
    Else
        Testtxt = True
    End If
End Function
Private Sub cmdInquire_Click()
    isEmpty= Testtxt(combo1(0).Text) or Testtxt(combo2(0).Text) or Testtxt(text1.Text)
    
    If isEmpty=False Then
	Msgbox"请输入查询条件",48,"提示"
    End If
End Sub

用这种方法使代码精简了不少，但是与最初的相比，用户不能直接明了的看出具体是哪个查询条件没选，各有各的好处。

组合查询也还是基本的查询，就是在写与数据库连接的语句时遇到了一些问题，细心一些就好了。

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