Errors in my SQLite Database for Android

I am having multiple issues with my SQLite Database with Android. I am new to developing and learning on my own. SO please use laymens terms and assume i do not know what you are talking about lol. Specifically i am having trouble wit the methods:

• getLast()


• deleteLast()


• getLatestSubjectForContact()


• getAllRows()


• isEmpty()

If you see any other errors i will accept feedback. Thanks for all help you can provide. here is my database code

package com.swavey.testing;

import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.provider.BaseColumns;
import android.security.KeyChain;

import java.util.Date;

/**
 * Created by Adrian on 11/5/2014.
 */
public class smsDatabase  {

    private static final String KEY_ID = "_id";
    private static final int COLUMN_ID =0;

    // database info
    public static final String DATABASE_NAME = "texts";
    public static final String DATABASE_TABLE = "mainTable";
    public static final int DATABASE_VERSION = 4;

    // list of fields
    public static final String KEY_ADDRESS = "address";
    public static final String KEY_BODY = "body";
    private static final String KEY_DATE = "date";
    private static final String KEY_READ = "read";
    private static final String KEY_THREADID = "thread_id";
    private static final String KEY_TYPE = "type";
    private static final String KEY_SEEN = "seen";

    //list of field numbers
    private static final int COL_ADDRESS = 1;
    private static final int COL_BODY = 2;
    private static final int COL_DATE = 3;
    private static final int COL_READ = 4;
    private static final int COL_THREADID = 5;
    private static final int COL_TYPE = 6;
    private static final int COL_SEEN = 7;

    //create string array of all fields;
    public static final String[] ALL_KEYS = new String[] {KEY_ID, KEY_ADDRESS, KEY_BODY, KEY_DATE,
         KEY_READ, KEY_THREADID, KEY_TYPE, KEY_SEEN};


    private static final String DATABASE_CREATE_SQL = "create table " + DATABASE_TABLE
            + " (" + KEY_ID + " integer primary key autoincrement, "
            +KEY_ADDRESS + " text not null, "
            +KEY_BODY + " text not null, "
            +KEY_DATE + " text not null, "
            +KEY_READ+ " text not null, "
            +KEY_THREADID+ " text not null, "
            +KEY_TYPE+ " text not null, "
            +KEY_SEEN+ " text not null"
            + ");";

    private final Context context;

    private DatabaseHelper dbHelper;
    private SQLiteDatabase db;

    public smsDatabase (Context cxt) {
        this.context = cxt;
        dbHelper = new DatabaseHelper(context);
    }

    //open database
    public void open() {
        db = dbHelper.getWritableDatabase();
    }
    //close database
    public void close() {
        dbHelper.close();
    }

    //returns a cursor with all rows loaded
    public Cursor getAllRows() {
        String where = null;
        Cursor cursor = db.query(true, DATABASE_TABLE, ALL_KEYS, where, null, null, null,
        null, null);

        if (cursor != null) {
            cursor.moveToFirst();
        }
        return cursor;
    }

    public boolean isEmpty() {
        String where = null;
        Cursor cursor = db.query(true, DATABASE_TABLE, ALL_KEYS, where, null, null, null,
                null, null);
        if (cursor!=null) return false;
        return true;
    }


    // insert sms into table
    public long insertSMS (SMS sms) {
        ContentValues iv = new ContentValues();
        iv.put(KEY_ADDRESS, sms.getAddress());
        iv.put(KEY_BODY, sms.getBody());
        iv.put(KEY_DATE, sms.getDate());
        iv.put(KEY_READ, sms.getRead());
        iv.put(KEY_THREADID, sms.getThread_id());
        iv.put(KEY_TYPE, sms.getType());
        iv.put(KEY_SEEN, sms.getSeen());




        return db.insert(DATABASE_TABLE, null, iv);
    }

    public Cursor getLast() {
        SMS txt = new SMS();
        String where = null;
        Cursor c = db.query(true, DATABASE_TABLE,ALL_KEYS, where, null, null, null, null, null);
        c.moveToLast();
        return c;

    }

    public void deleteLast() {
        String where = null;
        Cursor c = db.query(true, DATABASE_TABLE,ALL_KEYS, where, null, null, null, null, null);
        String las = Integer.toString(c.getCount());
        db.delete(DATABASE_TABLE, KEY_ID + "=" + las, null);
    }

    public void deleteRow(String address, String date, String body ) {
        db.delete(DATABASE_TABLE, KEY_ADDRESS + "=" + address +" and " + KEY_DATE + "=" +
        date + " and " + KEY_BODY + "=" + body, null);
    }

    public String getLatestSubjectForContact() {
        Cursor c = getLast();
        String sub = c.getString(c.getColumnIndex("body"));
        if (sub.length() > 30) {
            sub = sub.substring(0, 30) + "...";
            return sub;
        }
        sub = sub +  "...";
        return sub;
    }

    private static class DatabaseHelper extends SQLiteOpenHelper {
        DatabaseHelper(Context context) {
            super(context, DATABASE_NAME, null, DATABASE_VERSION);
        }

        public void onCreate(SQLiteDatabase _db) {
            _db.execSQL(DATABASE_CREATE_SQL);
        }


        public void onUpgrade(SQLiteDatabase _db, int oldVersion, int newVersion) {
            _db.execSQL("DROP TABLE IF EXISTS "+ DATABASE_TABLE);
            onCreate(_db);
        }
    }
}