如何确定VB.net中是否已经存在记录?
我正在用Access数据库做一个VB,我想创建一个按钮。哪个savebutton检查尝试插入的数据在何处重复或与我的数据库不比较 这是我的代码,问题是无论我输入什么,它只显示用户已经存在如何确定VB.net中是否已经存在记录?,vb.net,ms-access,Vb.net,Ms Access,我正在用Access数据库做一个VB,我想创建一个按钮。哪个savebutton检查尝试插入的数据在何处重复或与我的数据库不比较 这是我的代码,问题是无论我输入什么,它只显示用户已经存在 Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click MyConn = New OleDbConnection MyConn.ConnectionString = connString
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
MyConn = New OleDbConnection
MyConn.ConnectionString = connString
MyConn.Open()
If (ComboBox2.Text = "") And (ComboBox3.Text = "")
And (TextBox3.Text = "") And (ComboBox4.Text = "")
Then
MsgBox("Please fill-up all fields!")
Else
Dim theQuery As String = ("SELECT * FROM Table1
WHERE"" [Subject_Code]=@Subject_Code ,[Day]=@Day,
[Times]=@Times , [Lecture]=@Lecture and [Class_Room]=@Class_Room""")
Dim cmd1 As OleDbCommand = New OleDbCommand(theQuery, MyConn)
cmd1.Parameters.AddWithValue("@Subject_Code", TextBox6.Text)
cmd1.Parameters.AddWithValue("@Day", ComboBox2.Text)
cmd1.Parameters.AddWithValue("@Times", ComboBox3.Text)
cmd1.Parameters.AddWithValue("@Lecture", TextBox3.Text)
cmd1.Parameters.AddWithValue("@Class_Room", ComboBox4.Text)
Using reader As OleDbDataReader = cmd1.ExecuteReader()
If reader.HasRows Then
'User already exists
MsgBox("User Already Exist!")
Else
Dim Update As String = "INSERT INTO [Table1]
([Subject_Code], [Subject],
[Day], [Times], [Level],[Semester], [Lecture],[Class], [Class_Room])
VALUES (?,?,?,?,?,?,?,?,?)"
Using cmd = New OleDbCommand(Update, MyConn)
cmd.Parameters.AddWithValue("@p1", TextBox6.Text)
cmd.Parameters.AddWithValue("@p2", TextBox1.Text)
cmd.Parameters.AddWithValue("@p3", ComboBox2.Text)
cmd.Parameters.AddWithValue("@p4", ComboBox3.Text)
cmd.Parameters.AddWithValue("@p5", ComboBox1.Text)
cmd.Parameters.AddWithValue("@p6", ComboBox6.Text)
cmd.Parameters.AddWithValue("@p7", TextBox3.Text)
cmd.Parameters.AddWithValue("@p8", ComboBox5.Text)
cmd.Parameters.AddWithValue("@p9", ComboBox4.Text)
MsgBox("New Data Is Saved")
cmd.ExecuteNonQuery()
End Using
End If
End Using
End If
首先,快速查看您的theQuery变量,它可能只是从您键入它的位置发生了格式错误,但如果不尝试:
Dim theQuery As String = "SELECT * FROM Table1 " &
"WHERE [Subject_Code] = @Subject_Code " &
"AND [Day] = @Day " &
"AND [Times] = @Times " &
"AND [Lecture] = @Lecture " &
"AND [Class_Room] = @Class_Room"
您对预先存在的用户的检查基于5个字段,新数据的插入有9个字段。在不了解业务案例的情况下,我无法确定这是否正确,或者缺少的4个字段是否对检查非常重要,并导致返回意外的行
就我个人而言,我的下一步将是:
“
在您选择的字符串中做了什么?@Clavert这里有一条不成文的规则:避免使用紧急
。@reporter:它实际上是;-)
。所有那些WHERE
子句不都需要与和
连接吗?为什么不在表级别创建索引以防止重复?