SQLite add column, keep data

I have a database with 4 columns:

@Override
public void onCreate(SQLiteDatabase database) {
        database.execSQL("CREATE TABLE " + DATABASENAME + " (name TEXT, latitude REAL, longitude REAL, country TEXT);");
}

Now I want to add another column, but keep the rows that are already in the database. How should I do this? I can't find any useful references to this.

@Override
public void onUpgrade(SQLiteDatabase db, int arg1, int arg2) {
    //What to do here?
}

EDIT

I have modified my onCreate to:

@Override
public void onCreate(SQLiteDatabase database) {
    database.execSQL("CREATE TABLE " + DATABASENAME + " (name TEXT, latitude REAL, longitude REAL, country TEXT, code TEXT);");
}

and my onUpgrade to:

@Override
public void onUpgrade(SQLiteDatabase db, int arg1, int arg2) {
    Logger.log("Updating userstations database from " + arg1 + " to " + arg2 + ".");
    if (arg1 == 2 && arg2 == 3) {
        db.execSQL("ALTER 开发者_开发百科TABLE " + DATABASENAME + " ADD COLUMN code TEXT;");
    } else if(arg1 == 1){
        db.execSQL("DROP TABLE IF EXISTS " + DATABASENAME);
    }
    onCreate(db);
}

However, now I get this stacktrace:

10-01 21:24:19.581: ERROR/Database(21434): Failure 1 (table userstations already exists) on 0x19c378 when preparing 'CREATE TABLE userstations (name TEXT, latitude REAL, longitude REAL, country TEXT, code TEXT);'.
10-01 21:24:19.611: ERROR/SQLiteOpenHelper(21434): Couldn't open userstations for writing (will try read-only):
10-01 21:24:19.611: ERROR/SQLiteOpenHelper(21434): android.database.sqlite.SQLiteException: table userstations already exists: CREATE TABLE userstations (name TEXT, latitude REAL, longitude REAL, country TEXT, code TEXT);
10-01 21:24:19.611: ERROR/SQLiteOpenHelper(21434):     at android.database.sqlite.SQLiteDatabase.native_execSQL(Native Method)
10-01 21:24:19.611: ERROR/SQLiteOpenHelper(21434):     at android.database.sqlite.SQLiteDatabase.execSQL(SQLiteDatabase.java:1763)
10-01 21:24:19.611: ERROR/SQLiteOpenHelper(21434):     at com.myapp.myapp.databases.UserStationsOpenHelper.onCreate(UserStationsOpenHelper.java:25)
10-01 21:24:19.611: ERROR/SQLiteOpenHelper(21434):     at com.myapp.myapp.databases.UserStationsOpenHelper.onUpgrade(UserStationsOpenHelper.java:36)
10-01 21:24:19.611: ERROR/SQLiteOpenHelper(21434):     at android.database.sqlite.SQLiteOpenHelper.getWritableDatabase(SQLiteOpenHelper.java:132)
10-01 21:24:19.611: ERROR/SQLiteOpenHelper(21434):     at android.database.sqlite.SQLiteOpenHelper.getReadableDatabase(SQLiteOpenHelper.java:187)
10-01 21:24:19.611: ERROR/SQLiteOpenHelper(21434):     at com.myapp.myapp.databases.UserStationsOpenHelper.getStations(UserStationsOpenHelper.java:43)
10-01 21:24:19.611: ERROR/SQLiteOpenHelper(21434):     at com.myapp.myapp.Data.readUserStations(Data.java:369)
10-01 21:24:19.611: ERROR/SQLiteOpenHelper(21434):     at com.myapp.myapp.Data.getUserStations(Data.java:210)
10-01 21:24:19.611: ERROR/SQLiteOpenHelper(21434):     at com.myapp.myapp.stationstab.StationsActivity.newStations(StationsActivity.java:190)
10-01 21:24:19.611: ERROR/SQLiteOpenHelper(21434):     at com.myapp.myapp.stationstab.StationsActivity.refresh(StationsActivity.java:129)
10-01 21:24:19.611: ERROR/SQLiteOpenHelper(21434):     at com.myapp.myapp.stationstab.StationsActivity.onCreate(StationsActivity.java:108)
10-01 21:24:19.611: ERROR/SQLiteOpenHelper(21434):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
10-01 21:24:19.611: ERROR/SQLiteOpenHelper(21434):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1722)
10-01 21:24:19.611: ERROR/SQLiteOpenHelper(21434):     at android.app.ActivityThread.startActivityNow(ActivityThread.java:1598)
10-01 21:24:19.611: ERROR/SQLiteOpenHelper(21434):     at android.app.LocalActivityManager.moveToState(LocalActivityManager.java:127)
10-01 21:24:19.611: ERROR/SQLiteOpenHelper(21434):     at android.app.LocalActivityManager.startActivity(LocalActivityManager.java:339)
10-01 21:24:19.611: ERROR/SQLiteOpenHelper(21434):     at com.myapp.myapp.stationstab.StationsActivityGroup.onCreate(StationsActivityGroup.java:38)
10-01 21:24:19.611: ERROR/SQLiteOpenHelper(21434):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
10-01 21:24:19.611: ERROR/SQLiteOpenHelper(21434):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1722)
10-01 21:24:19.611: ERROR/SQLiteOpenHelper(21434):     at android.app.ActivityThread.startActivityNow(ActivityThread.java:1598)
10-01 21:24:19.611: ERROR/SQLiteOpenHelper(21434):     at android.app.LocalActivityManager.moveToState(LocalActivityManager.java:127)
10-01 21:24:19.611: ERROR/SQLiteOpenHelper(21434):     at android.app.LocalActivityManager.startActivity(LocalActivityManager.java:339)
10-01 21:24:19.611: ERROR/SQLiteOpenHelper(21434):     at android.widget.TabHost$IntentContentStrategy.getContentView(TabHost.java:654)
10-01 21:24:19.611: ERROR/SQLiteOpenHelper(21434):     at android.widget.TabHost.setCurrentTab(TabHost.java:326)
10-01 21:24:19.611: ERROR/SQLiteOpenHelper(21434):     at android.widget.TabHost.addTab(TabHost.java:216)
10-01 21:24:19.611: ERROR/SQLiteOpenHelper(21434):     at com.myapp.myapp.TreinVerkeer.setupTab(TreinVerkeer.java:131)
10-01 21:24:19.611: ERROR/SQLiteOpenHelper(21434):     at com.myapp.myapp.TreinVerkeer.initTabs(TreinVerkeer.java:108)
10-01 21:24:19.611: ERROR/SQLiteOpenHelper(21434):     at com.myapp.myapp.TreinVerkeer.onCreate(TreinVerkeer.java:62)
10-01 21:24:19.611: ERROR/SQLiteOpenHelper(21434):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
10-01 21:24:19.611: ERROR/SQLiteOpenHelper(21434):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1722)
10-01 21:24:19.611: ERROR/SQLiteOpenHelper(21434):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1784)
10-01 21:24:19.611: ERROR/SQLiteOpenHelper(21434):     at android.app.ActivityThread.access$1500(ActivityThread.java:123)
10-01 21:24:19.611: ERROR/SQLiteOpenHelper(21434):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:939)
10-01 21:24:19.611: ERROR/SQLiteOpenHelper(21434):     at android.os.Handler.dispatchMessage(Handler.java:99)
10-01 21:24:19.611: ERROR/SQLiteOpenHelper(21434):     at android.os.Looper.loop(Looper.java:123)
10-01 21:24:19.611: ERROR/SQLiteOpenHelper(21434):     at android.app.ActivityThread.main(ActivityThread.java:3835)
10-01 21:24:19.611: ERROR/SQLiteOpenHelper(21434):     at java.lang.reflect.Method.invokeNative(Native Method)
10-01 21:24:19.611: ERROR/SQLiteOpenHelper(21434):     at java.lang.reflect.Method.invoke(Method.java:507)
10-01 21:24:19.611: ERROR/SQLiteOpenHelper(21434):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:841)
10-01 21:24:19.611: ERROR/SQLiteOpenHelper(21434):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:599)
10-01 21:24:19.611: ERROR/SQLiteOpenHelper(21434):     at dalvik.system.NativeStart.main(Native Method)
10-01 21:24:19.621: DEBUG/AndroidRuntime(21434): Shutting down VM
10-01 21:24:19.621: WARN/dalvikvm(21434): threadid=1: thread exiting with uncaught exception (group=0x4018a560)
10-01 21:24:19.641: ERROR/AndroidRuntime(21434): FATAL EXCEPTION: main
10-01 21:24:19.641: ERROR/AndroidRuntime(21434): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.myapp.myapp/com.myapp.myapp.TreinVerkeer}: java.lang.RuntimeException: Unable to start activity ComponentInfo{com.myapp.myapp/com.myapp.myapp.stationstab.StationsActivityGroup}: java.lang.RuntimeException: Unable to start activity ComponentInfo{com.myapp.myapp/com.myapp.myapp.stationstab.StationsActivity}: android.database.sqlite.SQLiteException: Can't upgrade read-only database from version 2 to 3: /data/data/com.myapp.myapp/databases/userstations
10-01 21:24:19.641: ERROR/AndroidRuntime(21434):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1768)
10-01 21:24:19.641: ERROR/AndroidRuntime(21434):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1784)
10-01 21:24:19.641: ERROR/AndroidRuntime(21434):     at android.app.ActivityThread.access$1500(ActivityThread.java:123)
10-01 21:24:19.641: ERROR/AndroidRuntime(21434):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:939)
10-01 21:24:19.641: ERROR/AndroidRuntime(21434):     at android.os.Handler.dispatchMessage(Handler.java:99)
10-01 21:24:19.641: ERROR/AndroidRuntime(21434):     at android.os.Looper.loop(Looper.java:123)
10-01 21:24:19.641: ERROR/AndroidRuntime(21434):     at android.app.ActivityThread.main(ActivityThread.java:3835)
10-01 21:24:19.641: ERROR/AndroidRuntime(21434):     at java.lang.reflect.Method.invokeNative(Native Method)
10-01 21:24:19.641: ERROR/AndroidRuntime(21434):     at java.lang.reflect.Method.invoke(Method.java:507)
10-01 21:24:19.641: ERROR/AndroidRuntime(21434):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:841)
10-01 21:24:19.641: ERROR/AndroidRuntime(21434):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:599)
10-01 21:24:19.641: ERROR/AndroidRuntime(21434):     at dalvik.system.NativeStart.main(Native Method)
10-01 21:24:19.641: ERROR/AndroidRuntime(21434): Caused by: java.lang.RuntimeException: Unable to start activity ComponentInfo{com.myapp.myapp/com.myapp.myapp.stationstab.StationsActivityGroup}: java.lang.RuntimeException: Unable to start activity ComponentInfo{com.myapp.myapp/com.myapp.myapp.stationstab.StationsActivity}: android.database.sqlite.SQLiteException: Can't upgrade read-only database from version 2 to 3: /data/data/com.myapp.myapp/databases/userstations
10-01 21:24:19.641: ERROR/AndroidRuntime(21434):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1768)
10-01 21:24:19.641: ERROR/AndroidRuntime(21434):     at android.app.ActivityThread.startActivityNow(ActivityThread.java:1598)
10-01 21:24:19.641: ERROR/AndroidRuntime(21434):     at android.app.LocalActivityManager.moveToState(LocalActivityManager.java:127)
10-01 21:24:19.641: ERROR/AndroidRuntime(21434):     at android.app.LocalActivityManager.startActivity(LocalActivityManager.java:339)
10-01 21:24:19.641: ERROR/AndroidRuntime(21434):     at android.widget.TabHost$IntentContentStrategy.getContentView(TabHost.java:654)
10-01 21:24:19.641: ERROR/AndroidRuntime(21434):     at android.widget.TabHost.setCurrentTab(TabHost.java:326)
10-01 21:24:19.641: ERROR/AndroidRuntime(21434):     at android.widget.TabHost.addTab(TabHost.java:216)
10-01 21:24:19.641: ERROR/AndroidRuntime(21434):     at com.myapp.myapp.TreinVerkeer.setupTab(TreinVerkeer.java:131)
10-01 21:24:19.641: ERROR/AndroidRuntime(21434):     at com.myapp.myapp.TreinVerkeer.initTabs(TreinVerkeer.java:108)
10-01 21:24:19.641: ERROR/AndroidRuntime(21434):     at com.myapp.myapp.TreinVerkeer.onCreate(TreinVerkeer.java:62)
10-01 21:24:19.641: ERROR/AndroidRuntime(21434):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
10-01 21:24:19.641: ERROR/AndroidRuntime(21434):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1722)
10-01 21:24:19.641: ERROR/AndroidRuntime(21434):     ... 11 more
10-01 21:24:19.641: ERROR/AndroidRuntime(21434): Caused by: java.lang.RuntimeException: Unable to start activity ComponentInfo{com.myapp.myapp/com.myapp.myapp.stationstab.StationsActivity}: android.database.sqlite.SQLiteException: Can't upgrade read-only database from version 2 to 3: /data/data/com.myapp.myapp/databases/userstations
10-01 21:24:19.641: ERROR/AndroidRuntime(21434):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1768)
10-01 21:24:19.641: ERROR/AndroidRuntime(21434):     at android.app.ActivityThread.startActivityNow(ActivityThread.java:1598)
10-01 21:24:19.641: ERROR/AndroidRuntime(21434):     at android.app.LocalActivityManager.moveToState(LocalActivityManager.java:127)
10-01 21:24:19.641: ERROR/AndroidRuntime(21434):     at android.app.LocalActivityManager.startActivity(LocalActivityManager.java:339)
10-01 21:24:19.641: ERROR/AndroidRuntime(21434):     at com.myapp.myapp.stationstab.StationsActivityGroup.onCreate(StationsActivityGroup.java:38)
10-01 21:24:19.641: ERROR/AndroidRuntime(21434):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
10-01 21:24:19.641: ERROR/AndroidRuntime(21434):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1722)
10-01 21:24:19.641: ERROR/AndroidRuntime(21434):     ... 22 more
10-01 21:24:19.641: ERROR/AndroidRuntime(21434): Caused by: android.database.sqlite.SQLiteException: Can't upgrade read-only database from version 2 to 3: /data/data/com.myapp.myapp/databases/userstations
10-01 21:24:19.641: ERROR/AndroidRuntime(21434):     at android.database.sqlite.SQLiteOpenHelper.getReadableDatabase(SQLiteOpenHelper.java:199)
10-01 21:24:19.641: ERROR/AndroidRuntime(21434):     at com.myapp.myapp.databases.UserStationsOpenHelper.getStations(UserStationsOpenHelper.java:43)
10-01 21:24:19.641: ERROR/AndroidRuntime(21434):     at com.myapp.myapp

Please see this page for the syntax to create a new column on a table. Basically it is:

ALTER TABLE mytable ADD COLUMN mycolumn TEXT

In your onUpgrade method, it would look something like this:

@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
    String upgradeQuery = "ALTER TABLE mytable ADD COLUMN mycolumn TEXT";
    if (oldVersion == 1 && newVersion == 2)
         db.execSQL(upgradeQuery);
}

A better approach

@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
    switch (oldVersion) {
        case 1:
            db.execSQL(SQL_MY_TABLE);


        case 2:
            db.execSQL("ALTER TABLE myTable ADD COLUMN myNewColumn TEXT");

    }
}

Lets say in case 1, you upgraded to db version 2. You created a new table but forgot the myNewColumn you will see in case 2. What this will do is if you change the db version to 3, case 2 will get ran if its upgrading from 2 to 3.

I have not worked with android, but sqlite provides 'alter table' as most SQL implementations does:

SQLite alter table

The right way to add new column to DB, for example in version 2, would be:

@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
    if (oldVersion < 2) {
         db.execSQL("ALTER TABLE mytable ADD COLUMN mycolumn TEXT");
    }
}

It covers all pitfalls, including major issue with the selected answer: if a user goes from version 1 to 3 they will miss the upgrade query completely! These users will be in an awkward limbo where they are missing a few of the intermediate updates and do not have the expected sql schema.

Also don't forget to alter the create statement adding new column.