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VB图书管理系统源代码第4页

更新时间：2009-7-10: 来源：毕业论文

VB图书管理系统源代码第4页
Dim SqlString As String
    Dim OrderString As String
    Dim QueryString As String
    '这三个字符串变量用来存储查询语句
    'SqlString变量用来存储查询语句中除了ORDER BY子句之外的部分
    'OrderString变量用来存储ORDER BY子句
    'QueryString变量存储查询语句
    Private Sub 综合查询_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        '初始化列表“cmbBox查询表”
        Me.cmbBox查询表.Items.Add("读者信息")
        Me.cmbBox查询表.Items.Add("管理者信息")
        Me.cmbBox查询表.Items.Add("借阅信息")
        Me.cmbBox查询表.Items.Add("书籍信息")
        Me.cmbBox查询表.Items.Add("出版社信息")
        Me.cmbBox查询表.SelectedIndex = 0       '将列表的第一项设为选中项
    End Sub
    Private Sub cmbBox查询表_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cmbBox查询表.SelectedIndexChanged
        '在“cmbBox查询表”中选择一项作为查询表
        '则在“cmbBox查询依据”“cmbBox排序依据”将自动填充
        '查询表中的所有字段
        '保持数据表与字段二者的一致性
        Dim str_Table As String
        str_Table = Me.cmbBox查询表.SelectedItem
        If str_Table = "" Then Return
        Me.cmbBox查询依据.Items.Clear()
        Me.cmbBox排序依据.Items.Clear()
        Dim mySelectQuery As String = "SELECT * FROM " + str_Table
        Dim myCommand As New OleDb.OleDbCommand(mySelectQuery, Me.OleDbConnection1)
        If Me.OleDbConnection1.State = ConnectionState.Closed Then
            Me.OleDbConnection1.Open()
        End If
        Dim myReader As OleDb.OleDbDataReader
        myReader = myCommand.ExecuteReader
        Dim i As Integer
        For i = 0 To myReader.FieldCount - 1
            DataType(i) = myReader.GetFieldType(i).Name
            Me.cmbBox排序依据.Items.Add(myReader.GetName(i).ToString)
            Me.cmbBox查询依据.Items.Add(myReader.GetName(i).ToString)
        Next
        myReader.Close()
        Me.cmbBox查询依据.SelectedIndex = 0
        Me.cmbBox排序依据.SelectedIndex = 0
    End Sub
    Private Sub btn执行查询_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btn执行查询.Click
        If DataType(Me.cmbBox查询依据.SelectedIndex) = "Int32" Then
            SqlString = "SELECT * FROM " + Me.cmbBox查询表.Text + " WHERE"
            SqlString = SqlString + Me.cmbBox查询依据.Text + " " + _
            Me.cmbBox运算符.Text + " " + "(" + Me.edit指定值.Text + ")"
        ElseIf DataType(Me.cmbBox查询依据.SelectedIndex) = "String" Then
            SqlString = "SELECT * FROM " + Me.cmbBox查询表.Text + " WHERE"
            SqlString = SqlString + Me.cmbBox查询依据.Text + " " + _
            Me.cmbBox运算符.Text + " " + "'" + Me.edit指定值.Text + "'"
        ElseIf DataType(Me.cmbBox查询依据.SelectedIndex) = "Date" Then
            SqlString = "SELECT * FROM " + Me.cmbBox查询表.Text + " WHERE"
            SqlString = SqlString + Me.cmbBox查询依据.Text + " " + _
            Me.cmbBox运算符.Text + "Cdate(" + Me.edit指定值.Text + ")"
        End If
        OrderString = Me.cmbBox排序依据.Text
        QueryData(SqlString, OrderString)
        If Me.cmbBox查询表.Text = "读者信息" Then
            Me.OleDbInsertCommand2.CommandText = QueryString
        End If
        If Me.cmbBox查询表.Text = "管理者信息" Then
            Me.OleDbInsertCommand3.CommandText = QueryString
        End If
        If Me.cmbBox查询表.Text = "借阅信息" Then
            Me.OleDbInsertCommand4.CommandText = QueryString
        End If
        If Me.cmbBox查询表.Text = "书籍信息" Then
            Me.OleDbInsertCommand5.CommandText = QueryString
        End If
        If Me.cmbBox查询表.Text = "出版社信息" Then
            Me.OleDbInsertCommand1.CommandText = QueryString
        End If
        Try
            Me.LoadDataSet()    '尝试加载数据集
            Me.DataGrid1.DataMember = Me.cmbBox查询表.Text
        Catch eLoad As System.Exception
            System.Windows.Forms.MessageBox.Show(eLoad.Message)
        End Try
    End Sub

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