How to prevent to insert duplicate value in sqlite database (if duplicate then overwrite)

Question

I had created two table in my database, In both table I am inserting value at the same time, now what I want to do is that, I want to insert record in second table, but the condition is that, if there is two same record then I want insert only one record not duplicate value, In second table there is two field one is id and second is category, when user insert two same category that time I want to insert only one entry, below is my code which is not working properly, It insert all record accept duplicate value..

public long InsertCat(String idd, String cat) 
  { 
     try 
       {
        SQLiteDatabase db;
        long rows = 0;
        db = this.getWritableDatabase(); 
        ContentValues Val = new ContentValues();
        Val.put("IDD", idd); 
        Val.put("Category", cat);
        Cursor c = db.rawQuery("SELECT * FROM " + TABLE_CATEGER + " WHERE Category='"+cat+"'",null);
        while(c.moveToNext())
        {
            if(c.getString(0).equals(cat))
            {
                flag=true;
            }
        }           
        if(flag==true)
        {
          rows=db.update(TABLE_CATEGER, Val, "Category='"+cat+"'"  , null);     
          System.out.print(rows);
          db.close();
        }
        if(flag==false)
        {
            rows = db.insert(TABLE_CATEGER, null, Val);
            System.out.print(rows);             
            db.close();
        }
        return rows; // return rows inserted.
         } catch (Exception e) {
         return -1;
         }
        }

Answer 1

Put all your values inside ContentValues and then call this on writableDatabase

db.insertWithOnConflict(tableName, null, contentValues,SQLiteDatabase.CONFLICT_REPLACE);

EDIT:

Well all you need is only this part of code

    SQLiteDatabase db;
    long rows = 0;
    db = this.getWritableDatabase(); 
    ContentValues Val = new ContentValues();
    Val.put("IDD", idd); 
    Val.put("Category", cat);
    rows = db.insertWithOnConflict(tableName, null, contentValues,SQLiteDatabase.CONFLICT_REPLACE);

insertWithOnConflict methods follows the last parameter as the reaction algorithm when an duplicate row is Found. And for a duplicate row to be found, the primary keys has to clash. If all this satisfys the row would surely get Replaced :-/ If not something else is going wrong..

Answer 2

While creating your table, put constraint on your column(Primary key or Unique key).This will not only the duplicate value to be inserted into your database.