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SELECT TOP (1000) [company_id]
      ,[company_name]
      ,[caption]
      ,[address1]
      ,[address2]
      ,[mobileno]
      ,[email]
      ,[gstn]
      ,[CloudApi]
      ,[username]
      ,[password]
      ,[selectusertype]
      ,[uploadlogo]
      ,[activationkey]
  FROM [New_Restaurant_Application].[dbo].[add_profile]


What I have tried:

private void SignIn_Click(object sender, RoutedEventArgs e)
        {

            if (isValid())
            {
                SqlConnection conn = new SqlConnection(ConnectionString);
                conn.Open();
                //SqlCommand cmd = new SqlCommand("add_profile_details", conn);
                SqlDataAdapter sda = new SqlDataAdapter("SELECT username ='" + txtUsername.Text + "', password ='" + txtpassword.Password + "' , selectusertype = '"+cmboSelectusertype.Text+ "' from add_profile", conn);
                DataTable dt = new DataTable();  
                sda.Fill(dt);
                if (dt.Rows[0][0].ToString() == "")
                {
                    refresh();
                    Employee emp = new Employee();
                    emp.ShowDialog();
                }
                else
                {
                    MessageBox.Show("Invalid username or password"); 
                }
            }
Posted
Updated 2-Sep-22 4:21am

1 solution

Don't do it like that.
Never concatenate strings to build a SQL command. It leaves you wide open to accidental or deliberate SQL Injection attack which can destroy your entire database. Always use Parameterized queries instead.

When you concatenate strings, you cause problems because SQL receives commands like:
SQL
SELECT * FROM MyTable WHERE StreetAddress = 'Baker's Wood'
The quote the user added terminates the string as far as SQL is concerned and you get problems. But it could be worse. If I come along and type this instead: "x';DROP TABLE MyTable;--" Then SQL receives a very different command:
SQL
SELECT * FROM MyTable WHERE StreetAddress = 'x';DROP TABLE MyTable;--'
Which SQL sees as three separate commands:
SQL
SELECT * FROM MyTable WHERE StreetAddress = 'x';
A perfectly valid SELECT
SQL
DROP TABLE MyTable;
A perfectly valid "delete the table" command
SQL
--'
And everything else is a comment.
So it does: selects any matching rows, deletes the table from the DB, and ignores anything else.

So ALWAYS use parameterized queries! Or be prepared to restore your DB from backup frequently. You do take backups regularly, don't you?
 
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Comments
Richard MacCutchan 2-Sep-22 9:50am    
And a clear text password.

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