查詢表達式中字符串的語法錯誤

Question

即時通訊收到錯誤，其中“查詢EXPRESSION'用戶名=用戶'中字符串的語法錯誤我認為問題出在“ me.Username.tag”中，但即時通訊卡住了。

conn = New OleDbConnection(Get_Constring)
        conn.Open()
        cmd.Connection = conn
        cmd.CommandType = CommandType.Text
        cmd.CommandText = "select Username, fname,  lname, mname, [password], [level], Question, answer from Instructor where Username= '" & Me.txtusername.Tag

        dr = cmd.ExecuteReader
        If dr.HasRows Then
            While dr.Read
                Me.txtusername.Tag = dr("Username")
                Me.txtfname.Text = IIf(Not IsDBNull(dr("fname")), dr("fname"), "")
                Me.txtlname.Text = IIf(Not IsDBNull(dr("lname")), dr("lname"), "")
                Me.txtinitial.Text = IIf(Not IsDBNull(dr("mname")), dr("mname"), "")
                Me.txtpassword.Text = IIf(Not IsDBNull(dr("password")), dr("password"), "")
                Me.lbllevel.Text = IIf(Not IsDBNull(dr("level")), dr("level"), "")
                Me.txtusername.Text = IIf(Not IsDBNull(dr("Username")), dr("Username"), "")
                Me.cmbquestion.Text = IIf(Not IsDBNull(dr("Question")), dr("Question"), "")
                Me.txtanswer.Text = IIf(Not IsDBNull(dr("answer")), dr("answer"), "")
            End While
        End If

Answer 1

您沒有在查詢中關閉引號：

where Username= '" & Me.txtusername.Tag

應該：

where Username= '" & Me.txtusername.Tag & "'"

重要提示 ：您的代碼可能容易受到SQL注入攻擊的攻擊。 請使用參數化查詢 。 像這樣：

cmd.CommandText = "select Username, fname,  lname, mname, [password], [level], Question, answer from Instructor where Username= @username"
Dim parameter As New SqlParameter()
parameter.ParameterName = "@username"
parameter.SqlDbType = SqlDbType.NVarChar
parameter.Value = Me.txtusername.Tag
cmd.Parameters.Add(parameter);

Answer 2

我認為問題是您沒有關閉單引號。

試試這個：

cmd.CommandText = "select Username, fname,  lname, mname, [password], [level], Question, answer from Instructor where Username= '" & Me.txtusername.Tag & "'"

Answer 3

您尚未關閉查詢末尾打開的單引號