how to check record exists

1. If you are not familiar with C# and sql, then you should go through Using Parameterized SQL[^] first.
2. Once you have completed Point 1, adapt the following code snippet to check if certain record exists in the database.

string selectSQL = "select count(*) from tablename where somefieldname = @somevalue";
SqlCommand cmd = new SqlCommand(selectSQL);
cmd.Parameters.AddWithValue("@somevalue", TextBox1.Text.Trim());
Int32 rowCount = (Int32) cmd.ExecuteScalar();

3. After Point 3,

if (rowCount == 0){
  // execute sql insert, adapt example in point 1
}
else
{
  // execute sql update, adapt example in point 1
}

End of lesson.