机房收费系统——组合查询

              机房收费系统中的组合查询也是一大亮点。简单的查询只有一个条件限制，机房收费系统中涉及到的最多的查询条件限制是三个，就一起来揭开他的庐山真面目吧！

【示例界面】

      

【查询流程】

【函数转换】

          【“与”、“或”函数转换】

      

<span style="font-size:18px;"><strong>Public Function relation(a As String) As String
        
            '转换或和与
            Select Case a
                Case "与"
                    relation = "and"
                Case "或"
                    relation = "or"
            End Select
            
                    
End Function</strong></span>

             【查询条件转换】

<strong>Public Function filename(strfilename As String)
        '将选择的查询条件转换为数据库中的字段名 
        Select Case strfilename
            Case "教师"
                filename = "userid"
            Case "注册日期"
                filename = "logindate"
            Case "注册时间"
                filename = "logintime"
            Case "注销日期"
                filename = "logoutdate"
            Case "注销时间"
                filename = "logouttime"
            Case "机器名"
                filename = "computer"
            End Select
            </strong>
End Function

【三行信息分情况可用】

<span style="font-size:18px;"><strong><span style="font-size:18px;">Private Sub cmdQuery_Click()
    Dim txtsql As String
    Dim msgtext As String
    Dim mrc As ADODB.Recordset
    Dim ctrl As Control</span><span style="font-size:24px;">
    
   </span><span style="font-size:18px;"> '第一行可用
    
    '判断第一行信息是否有空值
        If Trim(comField1.Text) = "" Or Trim(comOperate1.Text) = "" Or Trim(txtContent1.Text) = "" Then
                MsgBox "请填充完整信息", vbOKOnly + vbExclamation, "警告"
                Exit Sub
        End If
        
    '将第一行的信息连接到txtsql中
        txtsql = "select * from worklog_info where "
        txtsql = txtsql & filename(comField1.Text) & Trim(comOperate1.Text) & "'" & Trim(txtContent1.Text) & "'"
        
    '第二行可用
        If Trim(comRelation(0).Text) <> "" Then
        
            
    '判断第二行信息是否有空值
                If Trim(comField2.Text) = "" Or Trim(comOperate2.Text) = "" Or Trim(txtContent2.Text) = "" Then
                        
                        MsgBox "请填充完整信息", vbOKOnly + vbExclamation, "警告"
                        Exit Sub
                
                End If
                
                txtsql = txtsql & relation(comRelation(0).Text) & " " & filename(comField2.Text) & Trim(comOperate2.Text) & "'" & Trim(txtContent2.Text) & "'"
                        
                    
        End If
        
    '第三行可用
        If Trim(comRelation(1).Text) <> "" Then
            
            
    '判断第三行信息是否有空值
    
                If Trim(comField3.Text) = "" Or Trim(comOperate3.Text) = "" Or Trim(txtContent3.Text) = "" Then
                    MsgBox "请填充完整信息", vbOKOnly + vbExclamation, "警告"
                    Exit Sub
                End If
            
                txtsql = txtsql & " " & relation(comRelation(1).Text) & " " & filename(comField3.Text) & comOperate3.Text & "'" _
                    & txtContent3.Text & "'"
        End If
        
        Set mrc = Executesql(txtsql, msgtext)
        
     '当没有记录的时候
     
        If mrc.EOF Then
        
            MsgBox "没有此记录", vbOKOnly + vbExclamation, "警告"
            
     '清除一类控件
            For Each ctrl In Me.Controls
                    If TypeOf ctrl Is TextBox Or TypeOf ctrl Is ComboBox Then
                            ctrl.Text = ""
                    End If
            Next
            
     '清空myflexgrid控件
            MyFlexGrid.Clear
            Call Form_Load
            Exit Sub
        End If
        
        With MyFlexGrid
    
    '设置列宽度
                For i = 0 To 8
                    MyFlexGrid.ColWidth(i) = 1500
                Next i
                
    '添加第一行信息
                .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"
                
                
    '将查询到的信息添加到控件中
        Do While Not mrc.EOF
                .Rows = .Rows + 1
                .CellAlignment = 4
                On Error Resume Next
                .TextMatrix(.Rows - 1, 0) = Trim(mrc.Fields("serial"))
                .TextMatrix(.Rows - 1, 1) = Trim(mrc.Fields("userid"))
                .TextMatrix(.Rows - 1, 2) = Trim(mrc.Fields("level"))
                .TextMatrix(.Rows - 1, 3) = Trim(mrc.Fields("logindate"))
                .TextMatrix(.Rows - 1, 4) = Trim(mrc.Fields("logintime"))
                .TextMatrix(.Rows - 1, 5) = Trim(mrc.Fields("logoutdate"))
                .TextMatrix(.Rows - 1, 6) = Trim(mrc.Fields("logouttime"))
                .TextMatrix(.Rows - 1, 7) = Trim(mrc.Fields("computer"))
                .TextMatrix(.Rows - 1, 8) = Trim(mrc.Fields("status"))
               
                mrc.MoveNext
            Loop
            mrc.Close
        End With
    </span><span style="font-size:24px;">
End Sub</span></strong></span>

【总结】

       组合查询并不难，他就是将简单查询的条件由一个变为了两个、三个。将查询语句该连接的连接起来就行！不要把自己先吓到，敲代码之前先想想和简单查询的相似之处和区别之处，遇到像“或”、“与”这类的汉字时无法直接连接，就要去考虑用自定义函数去转换！努力建立自己的知识网ing~