Does an ADO.NET DataReader read a whole row, or does it only read the columns you "Get"?

Question

If I do something like this:

using (SqlCommand cmd = new SqlCommand("SELECT * FROM TBL"))
{
    using (SqlDataReader reader = cmd.ExecuteReader())
    {
        while (reader.Read())
        {
            string s = reader.GetString(7);
        }
    }
}

does the Read() call read the entire row into memory, or does the GetString(7) call mean that the reader only ever reads the data in column 7?

Answer 1

it reads the whole row on the read operation.

Answer 2

I think you are looking for the ExecuteScalar method of the datareader and you want to specify your columns in your sql command.