机房收费系统（三）-组合查询

【前言】
一拖再拖，组合查询终于做完了，并且弄明白了其中的含义。下面就以操作员的工作记录窗体为例，来总结一下组合查询吧！
【内容】
组合查询：
第一行（可单独查询）即为第一个条件，第二行为第二个条件，第三行为第三个条件。利用“组合关系”控件将条件连接起来，进行组合查询。

导图

这张导图是我看了好多大佬的博客，和自己的思考之后画出来的，可能某个地方还不是理解的很透彻，望指点！

查询代码

Private Sub cmdInquiry_Click()

Dim txtSQL1 As String
Dim txtSQL2 As String
Dim txtSQL3 As String
Dim MsgText As String
Dim mrc As ADODB.Recordset
Dim a, b, c As String
    
    '给变量a赋值（当字段1选择日期、时间或非日期、非时间）
    If comboField1.Text = "日期" Or comboField1.Text = "时间" Then
        a = DTPicker1.Value
    Else
        a = txtInquiry1.Text
    End If
 
    '给变量b赋值（当字段2选择日期、时间或非日期、非时间）
    If comboField2.Text = "日期" Or comboField2.Text = "时间" Then
        b = DTPicker2.Value
    Else
        b = txtInquiry2.Text
    End If
    
    '给变量c赋值（当字段3选择日期、时间或非日期、非时间）
    If comboField3.Text = "日期" Or comboField3.Text = "时间" Then
        c = DTPicker3.Value
    Else
        c = txtInquiry3.Text
    End If
    
    '第一行内容是否输入完整
    If comboField1.Text = "" Then    '判断字段名是否为空
        MsgBox "请选择字段名！", 48, "警告"
        comboField1.SetFocus
        Exit Sub
    End If
    If comboOptSign1.Text = "" Then  '判断操作符是否为空
        MsgBox "请选择操作符！", 48, "警告"
        comboOptSign1.SetFocus
        Exit Sub
    End If
    If txtInquiry1.Text = "" Then    '判断要查询的内容是否为空
        MsgBox "请输入要查询的内容！", 48, "警告"
        txtInquiry1.SetFocus
        Exit Sub
    End If
    
    '第一个组合关系存在
    txtSQL1 = "select * from worklog_Info where " & field(comboField1.Text) _
            & " " & comboOptSign1.Text & " '" & Trim(a) & " '"
    Set mrc = ExecuteSQL(txtSQL1, MsgText)
    
    If Trim(comboGroup1.Text) <> "" Then
        If Trim(comboField2.Text) = "" Or Trim(comboOptSign2.Text) = "" Or Trim(b = "") Then
            MsgBox "请将第二行内容补充完整！", 48, "警告"
            Exit Sub
        Else
            txtSQL2 = txtSQL1 & " " & fieldname(comboGroup1.Text) & " " & field(comboField2.Text) _
                    & comboOptSign2.Text & "'" & Trim(b) & "'"
            Set mrc = ExecuteSQL(txtSQL2, MsgText)
        End If
    End If
    
    '第二个组合关系存在
    If Trim(comboGroup2.Text) <> "" Then
        If Trim(comboField3.Text) = "" Or Trim(comboOptSign3.Text) = "" Or Trim(c = "") Then
            MsgBox "请将第三行内容补充完整！", 48, "警告"
            Exit Sub
        Else
            txtSQL3 = txtSQL2 & " " & fieldname(comboGroup2.Text) & " " & _
                    field(comboField3.Text) & comboOptSign3.Text & "'" & Trim(c) & "'"
            Set mrc = ExecuteSQL(txtSQL3, MsgText)
        End If
    End If
    
    '判断要查找的内容是否存在
    If mrc.EOF Then
        MsgBox "没有您要查找的内容，请重新查询！", vbOKOnly + vbExclamation, "提示"
        MSFlexGrid1.Clear
        Exit Sub
    Else
        With MSFlexGrid1
            .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"
        End With
        
        Do While Not mrc.EOF
            With MSFlexGrid1
                .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) = Trim(mrc.Fields(5)) & ""
                .TextMatrix(.Rows - 1, 6) = Trim(mrc.Fields(6)) & ""
                .TextMatrix(.Rows - 1, 7) = Trim(mrc.Fields(7)) & ""
                .TextMatrix(.Rows - 1, 8) = Trim(mrc.Fields(8)) & ""
            End With
            mrc.MoveNext
        Loop
    End If
    mrc.Close
End Sub

在做的过程中必有的思考：在选择字段时，当选择了日期或者时间的时候，是不是用DTPicker1更好一点呢？想到这里了，就要动手去实践一下，这部分我也是试过多次，看了许多博客，才弄明白该如何去写代码。

思考：当字段选择了时间或日期，“要查询的内容”控件变为DTPicker1，否则还是用原来的文本框。
代码实现：变量
1.使用变量来代替文本框或DTPicker1；

Dim a, b, c As String
    '给变量a赋值（当字段1选择日期、时间或非日期、非时间）
    If comboField1.Text = "日期" Or comboField1.Text = "时间" Then
        a = DTPicker1.Value
    Else
        a = txtInquiry1.Text
    End If
    '给变量b赋值（当字段2选择日期、时间或非日期、非时间）
    If comboField2.Text = "日期" Or comboField2.Text = "时间" Then
        b = DTPicker2.Value
    Else
        b = txtInquiry2.Text
    End If
    '给变量c赋值（当字段3选择日期、时间或非日期、非时间）
    If comboField3.Text = "日期" Or comboField3.Text = "时间" Then
        c = DTPicker3.Value
    Else
        c = txtInquiry3.Text
    End If

2.查询语句中将“要查询的内容”字段用变量来代替；

txtSQL1 = "select * from worklog_Info where " & field(comboField1.Text) _
            & " " & comboOptSign1.Text & " '" & Trim(a) & " '"
    Set mrc = ExecuteSQL(txtSQL1, MsgText)
txtSQL2 = txtSQL1 & " " & fieldname(comboGroup1.Text) & " " & field(comboField2.Text) _
                    & comboOptSign2.Text & "'" & Trim(b) & "'"
            Set mrc = ExecuteSQL(txtSQL2, MsgText)
txtSQL3 = txtSQL2 & " " & fieldname(comboGroup2.Text) & " " & _
                    field(comboField3.Text) & comboOptSign3.Text & "'" & Trim(c) & "'"
            Set mrc = ExecuteSQL(txtSQL3, MsgText)

3.当选择了时间或日期，将DTPicker1字段显示，文本框隐藏。

If comboField1.Text = "注册日期" Then
        DTPicker1.Format = dtpShortDate
        txtInquiry1.Visible = False
        txtInquiry1.Enabled = False
        DTPicker1.Visible = True
        DTPicker1.Enabled = True
        
    ElseIf comboField1.Text = "注册时间" Then
        DTPicker1.Format = dtpShortTime
        txtInquiry1.Visible = False
        txtInquiry1.Enabled = False
        DTPicker1.Visible = True
        DTPicker1.Enabled = True
    ElseIf comboField1.Text = "注销日期" Then
        DTPicker1.Format = dtpShortDate
        txtInquiry1.Visible = False
        txtInquiry1.Enabled = False
        DTPicker1.Visible = True
        DTPicker1.Enabled = True
        
    ElseIf comboField1.Text = "注销时间" Then
        DTPicker1.Format = dtpShortTime
        txtInquiry1.Visible = False
        txtInquiry1.Enabled = False
        DTPicker1.Visible = True
        DTPicker1.Enabled = True
         
    ElseIf comboField1.Text <> "注册时间" And comboField1.Text <> "注册日期" _
           And comboField1.Text <> "注销日期" _
           And comboField1.Text <> "注销时间" Then
        DTPicker1.Visible = False
        DTPicker1.Enabled = False
        txtInquiry1.Visible = True
        txtInquiry1.Enabled = True
    End If