Is it possible to apply key's (Primary key, candidate key etc) in android while using database

Question

I am new to android and i have just learned how to use the database and i have a couple of questions:

1. How can we apply keys on the data in the database in android just like we give in Oracle database? Is it possible? If no please tell me why.

2. When i am deleting the first row in a database (Whose id is '1') the below rows id's are not coming in serial number i.e., id for the second row (Now first row) is '2' why not '1'.

Thank you

Answer 1

ok, from first,

1. "How can we apply keys on the data in the database in android just like we give in Oracle database? Is it possible? If no please tell me why."

Ans - We can apply the all rule which one applies to a any other database, like oracle, mysql etc... So you can have both concept of primary key and foreign key in Android's SQLite database.

2.When i am deleting the first row in a database (Whose id is '1') the below rows id's are not coming in serial number i.e., id for the second row (Now first row) is '2' why not '1'?

Ans : as per the database rules whenever you delete any records from row then its key is remains same, its not changed and whatever data after that records are also has a same key or ID so whenever you want to access that data the ID or key remain same.

EDIT: and If you want to modify that key or ID you can use UPDATE query for that.

EDIT: update(String table, ContentValues values, String whereClause, String[] whereArgs)

Updating Values

To execute an update statement, we have two ways:

 1. To execute db.execSQL
 2. To execute db.update method:



 public int UpdateEmp(Employee emp)

 {

   SQLiteDatabase db=this.getWritableDatabase();
   ContentValues cv=new ContentValues();
   cv.put(colName, emp.getName());
   cv.put(colAge, emp.getAge());
   cv.put(colDept, emp.getDept());
   return db.update(employeeTable, cv, colID+"=?", 
    new String []{String.valueOf(emp.getID())});   
 }

 The update method has the following parameters:

 1. String Table: The table to update a value in
 2. ContentValues cv: The content values object that has the new values
 3. String where clause: The WHERE clause to specify which record to update
 4. String[] args: The arguments of the WHERE clause


Convenience method for updating rows in the database.

Hope you will understand it.

Thanks,