c# - Check if row exists in database -

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I have a database and see if a specific record already exists or not. WHERE EMAIL = '"+ + + +" + + "' AND TELEPOOL = '" + + + + + +' '; Npgsql COMMAND COMMAND = New NPGSQL COMMAND: 

  string sql = "SELECT COUNT (*) tbl_student (Esquilla, con); int userCount = (int) command.ExecuteScalar (); if (user> gt; 0) {lblMessage.Text = "person already exists";}   
 The row that is not working The error message says that it is an invalid artist. I do not have any clue, please help me.    int userCount = (int) command.ExecuteScalar ( );    
 
 
 I suspect it is returning a  long  or try to use the same:  
  int userCount = Convert.ToInt32 (command.ExecuteScalar ());   
 If that does not work: Ask what it is:  
  object val = command.ExecuteScalar () Debug.WriteLine (val.GetType (). Full name);

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