这个 Visual Basic 6.0 代码有什么作用？

Question

下面的这个 Visual Basic 6.0 代码有什么作用？但是它已用于搜索功能，我不清楚。所以请解释一下它的作用。

Private Sub cmdSearch_Click()
    Dim key As Integer, str As String
    key = InputBox("Enter the Employee No whose details u want to know: ")
    Set rs = Nothing
    str = "select * from emp where e_no=" & key
    rs.Open str, adoconn, adOpenForwardOnly, adLockReadOnly
    txtNo.Text = rs(0)
    txtName.Text = rs(1)
    txtCity.Text = rs(2)
    txtDob.Text = rs(4)
    txtPhone.Text = rs(3)
    Set rs = Nothing
    str = "select * from emp"
    rs.Open str, adoconn, adOpenDynamic, adLockPessimistic
End Sub

Answer 1

尚未有人明确指出，rs 必须声明为As New RecordSet，这样Set rs = Nothing 的含义就与Set rs = New RecordSet 相同。

Answer 2

Private Sub cmdSearch_Click()
    Dim key As Integer, str As String
    key = InputBox("Enter the Employee No whose details u want to know: ") ''// query the user for a name
    Set rs = Nothing
    str = "select * from emp where e_no=" & key ''//create sql query on the fly
    rs.Open str, adoconn, adOpenForwardOnly, adLockReadOnly ''// create a connection to an sql database
    txtNo.Text = rs(0) ''//assign the results of the query to input fields or labels
    txtName.Text = rs(1)
    txtCity.Text = rs(2)
    txtDob.Text = rs(4)
    txtPhone.Text = rs(3)
    Set rs = Nothing
    str = "select * from emp"
    rs.Open str, adoconn, adOpenDynamic, adLockPessimistic ''// creates a new sql connection and load the whole emp table
End Sub

简短摘要：询问用户姓名并在标签或文本框中显示用户的数据。

Answer 3

它对数据库进行两次搜索。第一次搜索的结果用于填充一些文本框。第二次搜索的结果……好吧，我不知道他们在用它做什么。

Answer 4

它根据名为 e_no 的列从数据库中查找数据，将找到的行中的信息加载到 TextBox 控件中，然后重新查询数据库中的所有 emp 行。