java - Android Database SQLite Average -

i making app android sqlite database have 1 table , 2 columns: 1 names , other marks. also, can see information of database in listview , can add more elements it. how can make average of marks in database? , how can delete row?

i paste database helper

public class persondatabasehelper {

private static final string tag = persondatabasehelper.class.getsimplename();  // database configuration // if want onupgrade run change database_version private static final int database_version = 1; private static final string database_name = "mydatabase.db";  // table configuration private static final string table_name = "person_table";         // table name private static final string person_table_column_id = "_id";     // column named "_id" required cursor private static final string person_table_column_name = "person_name"; private static final string person_table_column_pin = "person_pin";  private databaseopenhelper openhelper; private sqlitedatabase database;  // wrapper class. means, outside world, communicate persondatabasehelper, // under hood databaseopenhelper class perform database crud operations public persondatabasehelper(context acontext) {      openhelper = new databaseopenhelper(acontext);     database = openhelper.getwritabledatabase(); }  public void insertdata (string apersonname, string apersonpin) {      // using contentvalues avoid sql format errors      contentvalues contentvalues = new contentvalues();      contentvalues.put(person_table_column_name, apersonname);     contentvalues.put(person_table_column_pin, apersonpin);      database.insert(table_name, null, contentvalues); }  public cursor getalldata () {      string buildsql = "select * " + table_name;      log.d(tag, "getalldata sql: " + buildsql);      return database.rawquery(buildsql, null); }  // databaseopenhelper class used perform database related operation  private class databaseopenhelper extends sqliteopenhelper {      public databaseopenhelper(context acontext) {         super(acontext, database_name, null, database_version);     }      @override     public void oncreate(sqlitedatabase sqlitedatabase) {         // create tables here          string buildsql = "create table " + table_name + "( " + person_table_column_id + " integer primary key, " +                 person_table_column_name + " text, " + person_table_column_pin + " text )";          log.d(tag, "oncreate sql: " + buildsql);          sqlitedatabase.execsql(buildsql);     }      @override     public void onupgrade(sqlitedatabase sqlitedatabase, int oldversion, int newversion) {         // database schema upgrade code goes here          string buildsql = "drop table if exists " + table_name;          log.d(tag, "onupgrade sql: " + buildsql);          sqlitedatabase.execsql(buildsql);       // drop previous table          oncreate(sqlitedatabase);               // create table beginning     } } 

}

use avarage (avg) aggregate function:

string query = "select avg("+person_table_column_pin +") "+table_name; 

and use sqlitedatabase.rawquery(string sql, string[] selectionargs) executing query. like:

database.rawquery(query, null); 

here can find sample fiddle.

while, deleting row, can use sqlitedatabase.delete(string table, string whereclause, string[] whereargs). example:

string = person_table_column_id+"=?"; string[] whereargs = new string[]{string.valueof(59)}; database.delete(table_name, where, whereargs); 

the above code delete row id 59.