VB—联合查询（查询学生信息实例）

       刚刚进行完了机房收费系统关于联合查询的部分，整个代码进行完了，才发现，联合查询的东西不是很多，要用到知识就只有一个写查询的语句，最难的地方就是分析查询情况，首先呢，简单介绍下我整个代码的思路，先列出查询时可能出现的情况：

      1.我们现在将第一句话当成一个查询的条件（卡号=1），仅用这一个条件进行查询

      2.将第一句话和第二句话联合起来，作为一个查询条件，进行查询（卡号=1与学号=1）

      3.将第一、二、三种加起来，视为一种查询的条件，进行查询

     分析完查询可能出现的几种情况，接下来，我们就开始写代码了！

Private Subcmdinquire_Click()
   
    Dim mrc As ADODB.Recordset
    Dim txtsql As String
    Dim msgtext As String
    '定义变量，将文本框中所输入的内容转化成字段输出来
    Dim FLD(0 To 4) As String
    Dim relation(0 To 1) As String
    '定义三种方式，判断文本框中输入的内容是否为空（格式：text1.text<>"")
    Dim ok1 As Boolean
    Dim ok2 As Boolean
    Dim ok3 As Boolean
 
    If cmbfield(0) <> "" Andcmbsign(0) <> "" And Trim(txtinquire(0).Text) <>"" Then
        ok1 = True
    Else
        ok1 = False
    End If
 
    If cmbfield(0) <> "" Andcmbsign(0) <> "" And Trim(txtinquire(0).Text) <>"" And cmbandor(0).Text <> "" And cmbfield(1).Text<> "" And cmbsign(1).Text <> "" AndTrim(txtinquire(1).Text) <> "" Then
        ok2 = True
    Else
        ok2 = False
    End If
 
    If cmbfield(0) <> "" Andcmbsign(0) <> "" And Trim(txtinquire(0).Text) <>"" And cmbandor(0).Text <> "" And cmbfield(1).Text<> "" And cmbsign(1).Text <> "" AndTrim(txtinquire(1).Text) <> "" And cmbfield(2).Text <>"" And cmbsign(2).Text <> "" AndTrim(txtinquire(2).Text) <> "" Then
        ok3 = True
    Else
        ok3 = False
    End If
定义一个变量FLD（注意：这里定义变量时所用的名称不能和ＶＢ里的关键字相重复）
　　将下拉菜单中所选择的东西转换成数据库中的字段，进行查询
    FLD(0) = "work_date"
    FLD(1) = "work_time"
    FLD(2) = "work_teacher"
    FLD(3) = "teacher_type"
    FLD(4) = "PC_name"
 
 
    relation(0) = " and "
    relation(1) = " or "
 
   
'当三种查询的条件都满足的时候
    If ok1 = True Then
        If ok2 = True Then
            If ok3 = True Then　　　　　　　　　　　　　　　　（注意：ListIndex属性的使用，这里使用listIndex是为了设定下拉菜单中返回值为字符串）
                txtsql = "select * fromwork_teacher where " & Trim(FLD(cmbfield(0).ListIndex)) & Trim(cmbsign(0).Text) & "'" &Trim(txtinquire(0).Text) & "'" &relation(cmbandor(0).ListIndex) & Trim(FLD(cmbfield(1).ListIndex)) &Trim(cmbsign(1).Text) & "'" & Trim(txtinquire(1).Text) &"'" & relation(cmbandor(0).ListIndex) &Trim(FLD(cmbfield(2).ListIndex)) & Trim(cmbsign(2).Text) &"'" & Trim(txtinquire(2).Text) & "'"
 
     写查询语句的时候更要注意符号的使用，尤其是单引号和双引号，在这里教给大家一个小方法，我们写完一句查询语句，然后可以 msgbox txtsql 设置一个立即窗口检查下自己是否书写正确！
            Else '满足两种查询条件
 
                txtsql = "select * fromwork_teacher where " & Trim(FLD(cmbfield(0).ListIndex)) &Trim(cmbsign(0).Text) & "'" & Trim(txtinquire(0).Text) &"'" & relation(cmbandor(0).ListIndex) & Trim(FLD(cmbfield(1).ListIndex))& Trim(cmbsign(1).Text) & "'" & Trim(txtinquire(1).Text)& "'"
            End If
        Else '满足一种查询条件
            txtsql = "select * fromwork_teacher where " & Trim(FLD(cmbfield(0).ListIndex)) &Trim(cmbsign(0).Text) & "'" & Trim(txtinquire(0).Text) &"'"
 
        End If
    Else  '没有输入完整的条件，查空
        Call checktext(0)
        Exit Sub
    End If
 
    Set mrc = ExecuteSQL(txtsql, msgtext)
 
    If mrc.EOF Then
 
        MsgBox "没有找到符合要求的结果！", vbOKOnly +vbInformation, "提示"
 
        With myflexgrid
            .Rows = 1
            .CellAlignment = 4
            .TextMatrix(0, 0) = "上机日期"
            .TextMatrix(0, 1) = "上机时间"
            .TextMatrix(0, 2) = "操作教师"
            .TextMatrix(0, 3) = "教师类型"
            .TextMatrix(0, 4) = "机器号"
 
        End With
        Exit Sub
    Else
        With myflexgrid
            .Rows = 1
            .CellAlignment = 4
            .TextMatrix(0, 0) = "上机日期"
            .TextMatrix(0, 1) = "上机时间"
            .TextMatrix(0, 2) = "操作教师"
            .TextMatrix(0, 3) = "教师类型"
            .TextMatrix(0, 4) = "机器号"
            Do While Not mrc.EOF
                .Rows = .Rows + 1
                .TextMatrix(.Rows - 1, 0) =mrc.Fields("work_date")
                .TextMatrix(.Rows - 1, 1) =mrc.Fields("work_time")
                .TextMatrix(.Rows - 1, 2) =mrc.Fields("work_teacher")
                .TextMatrix(.Rows - 1, 3) =mrc.Fields("teacher_type")
                .TextMatrix(.Rows - 1, 4) =mrc.Fields("PC_name")
                mrc.MoveNext
            Loop
        End With
        mrc.Close
 
    End If
 
End Sub
 
Private SubForm_Load()
cmbandor(0).AddItem"与"
cmbandor(0).AddItem"或"
 
cmbandor(1).AddItem"与"
cmbandor(1).AddItem"或"
 
cmbfield(0).AddItem"上机日期"
cmbfield(0).AddItem"上机时间"
cmbfield(0).AddItem"操作教师"
cmbfield(0).AddItem"教师类型"
cmbfield(0).AddItem"机器号"
 
 
cmbfield(1).AddItem"上机日期"
cmbfield(1).AddItem"上机时间"
cmbfield(1).AddItem"操作教师"
cmbfield(1).AddItem"教师类型"
cmbfield(1).AddItem"机器号"
 
cmbfield(2).AddItem"上机日期"
cmbfield(2).AddItem"上机时间"
cmbfield(2).AddItem"操作教师"
cmbfield(2).AddItem"教师类型"
cmbfield(2).AddItem"机器号"
 
cmbsign(0).AddItem"<"
cmbsign(0).AddItem">"
cmbsign(0).AddItem"="
cmbsign(0).AddItem"<>"
 
cmbsign(1).AddItem"<"
cmbsign(1).AddItem">"
cmbsign(1).AddItem"="
cmbsign(1).AddItem"<>"
 
 
cmbsign(2).AddItem"<"
cmbsign(2).AddItem">"
cmbsign(2).AddItem"="
cmbsign(2).AddItem"<>"
'
 
End Sub
Private Subchecktext(Index As Integer)
    Dim ok1 As Boolean
    Dim ok2 As Boolean
    Dim ok3 As Boolean
 
    If cmbfield(0) <> "" Andcmbsign(0) <> "" And Trim(txtinquire(0).Text) <>"" Then
        ok1 = True
    Else
        ok1 = False
    End If
 
    If cmbfield(0) <> "" Andcmbsign(0) <> "" And Trim(txtinquire(0).Text) <>"" And cmbandor(0).Text <> "" And cmbfield(1).Text<> "" And cmbsign(1).Text <> "" AndTrim(txtinquire(1).Text) <> "" Then
        ok2 = True
    Else
        ok2 = False
    End If
 
    If cmbfield(0) <> "" Andcmbsign(0) <> "" And Trim(txtinquire(0).Text) <> ""And cmbandor(0).Text <> "" And cmbfield(1).Text <>"" And cmbsign(1).Text <> "" AndTrim(txtinquire(1).Text) <> "" And cmbfield(2).Text <>"" And cmbsign(2).Text <> "" AndTrim(txtinquire(2).Text) <> "" Then
        ok3 = True
    Else
        ok3 = False
    End If
 
    If Not TestTxt(cmbfield(Index).Text) Then
        MsgBox "请选择字段名", vbOKOnly + vbInformation,"提示"
        cmbfield(Index).SetFocus
        Exit Sub
    End If
    If Not TestTxt(cmbsign(Index).Text) Then
        MsgBox "请选择操作符", vbOKOnly + vbInformation,"提示"
        cmbsign(Index).SetFocus
        Exit Sub
    End If
    If Not TestTxt(txtinquire(Index).Text) Then
        MsgBox "请输入要查询的内容", vbOKOnly +vbInformation, "提示"
        txtinquire(Index).SetFocus
        Exit Sub
    End If
 
End Sub

     到这了，所有的功能就能全部实现了，看下是不是很简单呢！ 如果谁有更好的方法欢迎指点批评！