VB查询数据库之组合查询——机房收费总结（二）

在机房收费系统中，组合查询用的还是挺多的，像上机状态查询窗体、学生上机统计信息窗体、操作员工记录窗体、基本信息维护窗体。这其中，学生基本信息维护窗体中的东西比较多，就以它为例子，说说组合查询吧！

学生基本信息维护窗体如图所示：

先把代码放在下面，然后再解说：

Option Explicit
Private Sub cboField1_Click()       '把选择的字段转换成  sql语句中的字段
    If cboField1.Text = "卡号" Then cboField1.Tag = "cardNo"
    If cboField1.Text = "学号" Then cboField1.Tag = "studentNo"
    If cboField1.Text = "姓名" Then cboField1.Tag = "studentName"
    If cboField1.Text = "性别" Then cboField1.Tag = "sex"
    If cboField1.Text = "学院" Then cboField1.Tag = "college"
    If cboField1.Text = "专业" Then cboField1.Tag = "major"
    If cboField1.Text = "年级" Then cboField1.Tag = "grade"
    If cboField1.Text = "班级" Then cboField1.Tag = "class"
End Sub

Private Sub cboField2_Click()        '把选择的字段转换成  sql语句中的字段
    If cboField2.Text = "卡号" Then cboField2.Tag = "cardNo"
    If cboField2.Text = "学号" Then cboField2.Tag = "studentNo"
    If cboField2.Text = "姓名" Then cboField2.Tag = "studentName"
    If cboField2.Text = "性别" Then cboField2.Tag = "sex"
    If cboField2.Text = "学院" Then cboField2.Tag = "college"
    If cboField2.Text = "专业" Then cboField2.Tag = "major"
    If cboField2.Text = "年级" Then cboField2.Tag = "grade"
    If cboField2.Text = "班级" Then cboField2.Tag = "class"
End Sub

Private Sub cboField3_Click()        '把选择的字段转换成  sql语句中的字段
    If cboField3.Text = "卡号" Then cboField3.Tag = "cardNo"
    If cboField3.Text = "学号" Then cboField3.Tag = "studentNo"
    If cboField3.Text = "姓名" Then cboField3.Tag = "studentName"
    If cboField3.Text = "性别" Then cboField3.Tag = "sex"
    If cboField3.Text = "学院" Then cboField3.Tag = "college"
    If cboField3.Text = "专业" Then cboField3.Tag = "major"
    If cboField3.Text = "年级" Then cboField3.Tag = "grade"
    If cboField3.Text = "班级" Then cboField3.Tag = "class"
End Sub

Private Sub cboMode1_Click()            '把选择的字段的组合关系转换成SQL中的组合关系关键字，后面可以直接写入查询语句
    If cboMode1.Text = "与" Then cboMode1.Tag = "and"
    If cboMode1.Text = "或" Then cboMode1.Tag = "or"

    cboField2.Visible = True
    cboSign2.Visible = True
    txtInquire2.Visible = True
    cboMode2.Visible = True
End Sub

Private Sub cboMode2_Click()            '把选择的字段组合关系转换成SQL中的组合关系关键字，后面可以直接写入查询语句
    If cboMode2.Text = "与" Then cboMode2.Tag = "and"
    If cboMode2.Text = "或" Then cboMode2.Tag = "or"

    cboField3.Visible = True
    cboSign3.Visible = True
    txtInquire3.Visible = True
End Sub

Private Sub cmdClear_Click()     '清空所有的属性
    cboField1.Text = ""
    cboField2.Text = ""
    cboField3.Text = ""
    cboSign1.Text = ""
    cboSign2.Text = ""
    cboSign3.Text = ""
    txtInquire1.Text = ""
    txtInquire2.Text = ""
    cboMode1.Text = ""
    cboMode2.Text = ""

    cboField2.Visible = False       '把多查询条件字段先隐藏'隐藏起多字段，这样刚刚开始，只显示第一条查询，如果需要，选择"与"或者"或"，显示下一条字段，同理显示第三条字段。无形中告诉使用者，不要空掉第二条字段，只用一三条，这样会给编码带来麻烦的。
    cboSign2.Visible = False
    txtInquire2.Visible = False
    cboMode2.Visible = False

    cboField3.Visible = False
    cboSign3.Visible = False
    txtInquire3.Visible = False

    myFlexGrid.Clear
End Sub

Private Sub cmdcharge_Click()
    Dim txtSQL As String
    Dim MsgText As String
    Dim mrcSD As ADODB.Recordset

    txtSQL = "select * from student_Info where studentNo='" & Trim(myFlexGrid.TextMatrix(myFlexGrid.RowSel, 0)) & "'"
    Set mrcSD = ExecuteSQL(txtSQL, MsgText)

        If mrcSD.RecordCount = 0 Then
        MsgBox "请选中一条记录!", vbOKCancel + vbExclamation, "警告"
        Exit Sub
    End If

    frmModifyStudentLog.Show'显示查询窗体
End Sub

Private Sub cmdExit_Click()
    Unload Me
End Sub

Private Sub cmdselect_Click()
    Dim txtSQL As String
    Dim MsgText As String
    Dim mrc As ADODB.Recordset

    If cboMode1.Text = "" Then
        MsgBox "请输入需要查询的字段", vbOKOnly + vbExclamation, "警告"
       Unload Me
    End If

    '首先写一个不完全的SQL语句，一会儿补充
    txtSQL = "select * from student_Info where (" & cboField1.Tag & cboSign1.Text & "'" & txtInquire1.Text & "'"

    If cboMode1.Text <> "" Then      '检验第二个组合字段的正确性
        If cboField2.Text = "" Then
            MsgBox "请选择字段名！", vbOKOnly + vbExclamation, "警告"
            cboField2.SetFocus
            Exit Sub
        End If
        If cboSign2.Text = "" Then
            MsgBox "请输入操作符！", vbOKOnly + vbExclamation, "警告"
            cboSign2.SetFocus
            Exit Sub
        End If
        If txtInquire2.Text = "" Then
            MsgBox "请输入要查询的内容", vbOKOnly + vbExclamation, "警告"
            txtInquire2.SetFocus
            Exit Sub
        End If

        '第二个组合字段正确，开始添加信息
        txtSQL = txtSQL & " " & cboMode1.Tag & " " & cboField2.Tag & cboSign2.Text & "'" & txtInquire2.Text & "'"
    End If

    If cboMode2.Text <> "" Then     '检验第三组 组合字段的正确性
        If cboField3.Text = "" Then
            MsgBox "请选择字段名！", vbOKOnly + vbExclamation, "警告"
            cboField3.SetFocus
            Exit Sub
        End If
        If cboSign3.Text = "" Then
            MsgBox "请输入操作符！", vbOKOnly + vbExclamation, "警告"
            cboSign3.SetFocus
            Exit Sub
        End If
        If txtInquire3.Text = "" Then
            MsgBox "请输入要查询的内容", vbOKOnly + vbExclamation, "警告"
            txtInquire3.SetFocus
            Exit Sub
        End If

        '第三个组合字段正确，开始添加信息
        txtSQL = txtSQL & " " & cboMode2.Tag & " " & cboField3.Tag & cboSign3.Text & "'" & txtInquire3.Text & "'"
    End If

    txtSQL = txtSQL & ") "   '把SQL语句补充完整
    'Debug.Print txtSQL   用于调试程序使用
    Set mrc = ExecuteSQL(txtSQL, MsgText)

    If mrc.RecordCount = 0 Then         '如果要查询的结果为空，则提醒用户
        myFlexGrid.Clear
        MsgBox "结果集为空!", vbOKOnly + vbExclamation, "警告"
        Exit Sub
    End If

    With myFlexGrid         '把标题写上
        .Row = 0
        .TextMatrix(.Row, 0) = "学号"
        .TextMatrix(.Row, 1) = "姓名"
        .TextMatrix(.Row, 2) = "卡号"
        .TextMatrix(.Row, 3) = "余额"
        .TextMatrix(.Row, 4) = "学院"
        .TextMatrix(.Row, 5) = "年级"
        .TextMatrix(.Row, 6) = "班级"
        .TextMatrix(.Row, 7) = "性别"
        .TextMatrix(.Row, 8) = "状态"
        .TextMatrix(.Row, 9) = "备注"
    End With

    myFlexGrid.Rows = mrc.RecordCount + 1           '设置大小

    With myFlexGrid         '对查询到的结果进行遍历，显示出来
        .Row = 0
        While mrc.EOF = False
            .Row = .Row + 1
            .TextMatrix(.Row, 0) = "  " & mrc.Fields(1)
            .TextMatrix(.Row, 1) = "  " & mrc.Fields(2)
            .TextMatrix(.Row, 2) = "  " & mrc.Fields(0)
            .TextMatrix(.Row, 3) = "  " & mrc.Fields(7)
            .TextMatrix(.Row, 4) = "  " & mrc.Fields(4)
            .TextMatrix(.Row, 5) = "  " & mrc.Fields(5)
            .TextMatrix(.Row, 6) = "  " & mrc.Fields(6)
            .TextMatrix(.Row, 7) = "  " & mrc.Fields(3)
            .TextMatrix(.Row, 8) = "  " & mrc.Fields(11)
            .TextMatrix(.Row, 9) = "  " & mrc.Fields(8)
            mrc.MoveNext
        Wend
    End With
End Sub

Private Sub Form_Load()
    cboField1.AddItem "卡号"
    cboField1.AddItem "学号"
    cboField1.AddItem "姓名"
    cboField1.AddItem "性别"
    cboField1.AddItem "学院"
    cboField1.AddItem "专业"
    cboField1.AddItem "年级"
    cboField1.AddItem "班级"

    cboField2.AddItem "卡号"
    cboField2.AddItem "学号"
    cboField2.AddItem "姓名"
    cboField2.AddItem "性别"
    cboField2.AddItem "学院"
    cboField2.AddItem "专业"
    cboField2.AddItem "年级"
    cboField2.AddItem "班级"

    cboField3.AddItem "卡号"
    cboField3.AddItem "学号"
    cboField3.AddItem "姓名"
    cboField3.AddItem "性别"
    cboField3.AddItem "学院"
    cboField3.AddItem "专业"
    cboField3.AddItem "年级"
    cboField3.AddItem "班级"

    cboSign1.AddItem "="
    cboSign1.AddItem "<"
    cboSign1.AddItem ">"
    cboSign1.AddItem "<>"

    cboSign2.AddItem "="
    cboSign2.AddItem "<"
    cboSign2.AddItem ">"
    cboSign2.AddItem "<>"

    cboSign3.AddItem "="
    cboSign3.AddItem "<"
    cboSign3.AddItem ">"
    cboSign3.AddItem "<>"

    cboMode1.AddItem "与"
    cboMode1.AddItem "或"

    cboMode2.AddItem "与"
    cboMode2.AddItem "或"
End Sub
  

在编写这个窗体的时候，刚开始总是无法查询，各种报错，后来，看了同学的博客，利用tag将文字语言转换为sql语言，直接写入查询语句，这就方便了很多。之后，在查询的时候，刚开始想直接在窗体中显示所有查询语句，但是，在执行的时候，往往因为第二条空着，而第三条能写入了查询条件而出错。各种限制方法非常麻烦，我就直接限制了窗体显示的语句条数，算是个“懒办法”吧！

这个窗体还真是用了不少时间，刚刚开始是因为不知道如何写查询语句，使用了tag之后，又出现了查询时遍历错误，总之，麻烦还是挺多的。不过，解决了一个窗体，其他的组合查询都差不多了。

我的总结，希望大家帮忙找出缺点，改正后一起进步。下一篇VB写入数据库。

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