如何在 android SQLite 中的现有表上添加列？

Question

how to add column in the existing table LOGIN. here's my sample code.

this is my DataBaseAdapter class:

public class DataBaseHelper extends SQLiteOpenHelper
{
    public DataBaseHelper(Context context, String name,CursorFactory factory, int version) 
    {
               super(context, name, factory, version);
    }
    // Called when no database exists in disk and the helper class needs
    // to create a new one.
    @Override
    public void onCreate(SQLiteDatabase _db) 
    {
            _db.execSQL(LoginDataBaseAdapter.DATABASE_CREATE);

    }
    // Called when there is a database version mismatch meaning that the version
    // of the database on disk needs to be upgraded to the current version.
    @Override
    public void onUpgrade(SQLiteDatabase _db, int _oldVersion, int _newVersion) 
    {
            // Log the version upgrade.
            Log.w("TaskDBAdapter", "Upgrading from version " +_oldVersion + " to " +_newVersion + ", which will destroy all old data");


            // Upgrade the existing database to conform to the new version. Multiple
            // previous versions can be handled by comparing _oldVersion and _newVersion
            // values.
            // The simplest case is to drop the old table and create a new one.
            _db.execSQL("DROP TABLE IF EXISTS " + "TEMPLATE");
            // Create a new one.
            onCreate(_db);
    }

this is my LoginDataBaseAdapter

public class LoginDataBaseAdapter 
{
        static final String DATABASE_NAME = "login.db";
        static final int DATABASE_VERSION = 1;
        public static final int NAME_COLUMN = 1;
        // TODO: Create public field for each column in your table.
        // SQL Statement to create a new database.
        static final String DATABASE_CREATE = "create table "+"LOGIN"+
                                     "( " +"ID"+" integer primary key autoincrement,"+ "USERNAME  text,PASSWORD text); ";
        // Variable to hold the database instance
        public  SQLiteDatabase db;
        // Context of the application using the database.
        private final Context context;
        // Database open/upgrade helper
        private DataBaseHelper dbHelper;
        public  LoginDataBaseAdapter(Context _context) 
        {
            context = _context;
            dbHelper = new DataBaseHelper(context, DATABASE_NAME, null, DATABASE_VERSION);
        }
        public  LoginDataBaseAdapter open() throws SQLException 
        {
            db = dbHelper.getWritableDatabase();
            return this;
        }
        public void close() 
        {
            db.close();
        }

        public  SQLiteDatabase getDatabaseInstance()
        {
            return db;
        }

        public void insertEntry(String userName,String password)
        {
           ContentValues newValues = new ContentValues();
            // Assign values for each row.
            newValues.put("USERNAME", userName);
            newValues.put("PASSWORD",password);

            // Insert the row into your table
            db.insert("LOGIN", null, newValues);
            ///Toast.makeText(context, "Reminder Is Successfully Saved", Toast.LENGTH_LONG).show();
        }
        public int deleteEntry(String UserName)
        {
            //String id=String.valueOf(ID);
            String where="USERNAME=?";
            int numberOFEntriesDeleted= db.delete("LOGIN", where, new String[]{UserName}) ;
           // Toast.makeText(context, "Number fo Entry Deleted Successfully : "+numberOFEntriesDeleted, Toast.LENGTH_LONG).show();
            return numberOFEntriesDeleted;
        }   
        public String getSinlgeEntry(String userName1)
        {
            Cursor cursor=db.query("LOGIN", null, " USERNAME=?", new String[]{userName1}, null, null, null);
            if(cursor.getCount()<1) // UserName Not Exist
            {
                cursor.close();
                return "NOT EXIST";
            }
            cursor.moveToFirst();
            String password= cursor.getString(cursor.getColumnIndex("PASSWORD"));
            cursor.close();
            return password;                
        }
        public void  updateEntry(String userName,String password)
        {
            // Define the updated row content.
            ContentValues updatedValues = new ContentValues();
            // Assign values for each row.
            updatedValues.put("USERNAME", userName);
            updatedValues.put("PASSWORD",password);

            String where="USERNAME = ?";
            db.update("LOGIN",updatedValues, where, new String[]{userName});               
        }       
}

how can I add the columns FIRSTNAME(from TextView), LASTNAME(from TextView), DEPARTMENT(from Spinner).

Answer 1

You'll have to update your SQLite database version first of all, then that will run your onUpgrade() method, which will drop all of your data. Then the table will be remade with the new schema that you have defined in your DATABASE_CREATE string.

So the main issue that this comes with is that you'll have to find a way to recover the data that is already existing in the table as the table will be dropped. You do get to run onUpgrade before this happens though so use this method as a point to save any data you need to from the database.

static final int DATABASE_VERSION = 2;

and update your database creation string.

Answer 2

You can also alter the existing table if all you want to do is add one or more columns. So say you want to add a new column named 'my_new_col' to a table named 'my_table', in addition to updating your database version number from 1 to 2, you can update the table's schema without losing any data :

...
@Override
public void onUpgrade( SQLiteDatabase db, int oldVersion, int newVersion ) {
    switch( newVersion ) {

        case 2: /* this is your new version number */

            // ... Add new column 'my_new_col' to table 'my_table'
            db.execSQL( "alter table my_table add column my_new_col" ) ;
            break ;
    }
}

That's it. Of course you would want to define additional constraints on that new column and you'd want to ensure that the new column is included in the original table's creation in 'onCreate(...)'.

Answer 3

You have to do three things to successfully adding a column in existing table without losing previous data:

1. Upgrade your db version: as like:

    `static final int DB_VERSION = 2;`

2. Add the new Column in Database creation STATEMENT: as like, here new column is MEMBER_PHOTO :

   private static final String CREATE_TABLE = "create table "+ TABLE_MEMBER + "(" + MEMBER_ID + " INTEGER PRIMARY KEY AUTOINCREMENT, "+ MEMBER_NAME + " TEXT NOT NULL, " + MEMBER_PHOTO + " TEXT NOT NULL);";

3. At last in OnUpgrade method add the column in upgraded execute:

    @Override public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) { // TODO Auto-generated method stub // new Version 2: String sql = "ALTER TABLE " + TABLE_MEMBER + " ADD COLUMN " + "MEMBER_PHOTO" + " TEXT NOT NULL DEFAULT '' "; db.execSQL(sql); }