SQLite add column, keep data

Question

I have a database with 4 columns:

@Override
public void onCreate(SQLiteDatabase database) {
        database.execSQL(\"CREATE TABLE \" + DATABASENAME + \" (name          


        

Answer 1

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.

Answer 2

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

SQLite alter table

Answer 3

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);
}

Answer 4

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.