Invalid column name in SQL Select command

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hi dears,
I want read a table with "select * from ..." command in ASP.NET,
I wrote the code below:

C#

SqlConnection con = new SqlConnection(@"Data Source=.\sql2008;Initial Catalog=test;Integrated Security=true;");
  string str = "select * from tbluser where flduser='"+TextBox1.Text.Trim() +"' and fldpass=" + TextBox2.Text.Trim();

  SqlCommand command = new SqlCommand(str, con);
  con.Open();
  SqlDataReader reader = command.ExecuteReader();

  string selectedStudentName = Convert.ToString(reader);

what is my problem?
it's showed below error:
invalid coumn name

Posted 15-Dec-13 3:11am

hanis29268

Updated 15-Dec-13 3:25am

Mike Meinz

v3

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José Amílcar Casimiro 15-Dec-13 9:15am

Probably the "fldpass" field is a string and is also missing the limiter string.
You must be careful with sql injection.

Mike Meinz 15-Dec-13 9:18am

Please do not implement your web site using this code. A simple SQL Injection Attack will be able to destroy your database. Use SQLParameter Class to pass Textbox1.Text and Textbox2.Text to the SQL Select statement as parameters. This prevents SQL Injection attacks and provides better performance.

See Configuring Parameters and Parameter Data Types

[no name] 15-Dec-13 9:19am

i want show sql injection to my classmate,
so need to run above code,
but it's showed invalid column name

Mike Meinz 15-Dec-13 9:21am

You are missing the apostrophes surrounding Textbox2.Text value in the Select command.

string str = "select * from tbluser where flduser=" + "'" + TextBox1.Text.Trim() + "'" + " and fldpass=" + "'" + TextBox2.Text.Trim() + "'";

[no name] 15-Dec-13 9:23am

thanks Mike Meinz
but where is my result(record of table)??

Mike Meinz 15-Dec-13 9:30am

See Retrieving Data Using a DataReader

You must execute the Read method of reader class to retrieve the row and then retrieve each column from that row.

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OriginalGriff · Answer 1 · 2013-12-15T03:35:00

You can't just go:

C#

SqlDataReader reader = command.ExecuteReader();
string selectedStudentName = Convert.ToString(reader);

You need to actually read the values from the db, and specify which column you want as weel as (as Mike Meinz says) using a parametrized query.
Try this:

C#

string str = "select * from tbluser where flduser=@USER";
SqlCommand command = new SqlCommand(str, con);
con.Open();
command.Parameters.AddWithValue("@USER", TextBox1.Text.Trim());
SqlDataReader reader = command.ExecuteReader();
string selectedStudentName = "";
if (reader.Read())
   {
   selectedStudentName = (string) reader["NameOoColumnWithUserNameInIt"];
   }