How can i check if the database contains the rows stated or not?

Question

hi there..
i hav a problem here. I need to check the database if it contains the row of the attribute. If it doesnt not hav the row, i would then insert a new row into it, or else, i would only update the attribute. I have encountered a null pointer error and i've been trying to resolve it but i cant solve it. Here's my code..
"i" is the attribute i wan to check if it exist in the database.
"id" is the attribute i wan to check, from my JSP
String m = null;
String sql11 = "SELECT i from database WHERE i ='" + i+ "'";
System.out.println(sql11);
try {
db = new Database();
rs = db.readRequest(sql11);
if (rs != null && rs.next()) {
U u= new U();
u.setU(rs.getString("i"));
m = u.getU(); ==> this is the line tat's givin my null pointer
System.out.println(m);
db.close();
} catch (SQLException se) {
se.printStackTrace();
throw (new UserException("Unable to retrieve from Database!"));
} catch (Exception e) {
e.printStackTrace();
throw (new UserException("Unknow error encountered!"));
if (m.equals(id)){
//performs the updating of database
else if (m_userID.equals("nil")){
// performs the inserting of new row in the database
}*/

Answer 1

And what does getU() do?