我怎么知道从Java到SQL Server的SQL选择查询没有返回任何结果？

Question

I am trying to know if a SELECT query made from Java to SQL Server doesn't return any results, because I'm trying to do a "verification" in the database to know if a User already exists, so if the SELECT query returned false , for example, I know that the given user doesn't exist and I can add it to the database.

Connection c = ConexionSQL.Conexion.getConection();
try {
    Statement select = c.createStatement();
    ResultSet r = select.executeQuery("SELECT * FROM Usuario WHERE id="+id);

    if(r.next()) {
        //Show message that the user already Exists
    }
    else {
        //Add user to the database
    }
}
catch(Exception ex) {
    System.out.println("No se puedo realizar el select");
    ex.printStackTrace();
}

Answer 1

I am guessing that your code works, but instead of using r.next() you can use r.isBeforeFirst() , because if there's data, you won't have to backtrack to get it back.

In summary, isBeforeFirst() returns false if there cursor is not before the first row or if there are no rows.