Disallow duplicate records and check if database is available

I am creating a database and I'm inserting a row like so:

/* Add two DataSets to the Table. */
myDB.execSQL("INSERT INTO "
              + MY_DATABASE_TABLE
              + " (LastName, FirstName, Country, Age)"
              + " VALUES ('Gramlich', 'Nicolas', 'Germany', 20);");
 myDB.execSQL("INSERT INTO "
              + MY_DATABASE_TABLE
              + " (LastName, FirstName, Country, Age)"
              + " VALUES ('Doe', 'John', 'US', 34);");

I have two questions regarding the above code:

1. How do I disallow duplicate records? I want to check incoming data at the insert time. How can I achieve that? Should I use IF NOT EXISTS?

2. How can I check whether that dat开发者_如何学Pythonabase is available or not? So far, without any success, I've tried:

   private static String DB_PATH = "/data/data/YOUR_PACKAGE/databases/myDBName";
   private static String DB_NAME = "myDBName";
   
   private boolean checkDataBase() {
       SQLiteDatabase checkDB = null;
       try {
           checkDB = SQLiteDatabase.openDatabase(DB_PATH, null,
           SQLiteDatabase.OPEN_READONLY);
           checkDB.close();
       } catch (SQLiteException e) {
           // database doesn't exist yet.
       }
       return checkDB != null ? true : false;
   }
   

Any suggestions on how to achieve this?

---

to prevent duplicates create a UNIQUE INDEX on that table.

At runtime, you have at least two options:

1. let the index give you an exception if you attempt a duplicate, then catch that exception and do something else, or

2. Query the table pro-actively to see if the new record exists, and if you find it you know there is a duplicate, so do something else.

---

Here are a few suggestions:

1. When creating your tables, define the columns that you want to prevent duplicates as UNIQUE.
2. Your checkDataBase() method is a bit strange. Have you considered using the SQLiteOpenHelper class in your implementation to simplify things?

http://developer.android.com/reference/android/database/sqlite/SQLiteOpenHelper.html