如何在我已经创建的表中添加新列？

Question

I want to add a new column (item_price) in the already created table.I've tried some solutions using the onUpgrade method but still couldn't get it working.At first I literally added the column like a dummy then I saw posts that show how to use the onUpgrade method.

Here is my Constants class:

public class Constants {
public static final int DB_VERSION = 2;
public static  final String DB_NAME = "babyList";
public static final String TABLE_NAME = "baby_tbl";

public static final String KEY_ID = "id";
public static final String KEY_BABY_ITEM = "baby_item";
public static final String KEY_QTY_NUMBER = "quantity_number";
public static final String KEY_COLOR = "color";
public static final String KEY_ITEM_SIZE = "size";
public static final String KEY_DATE_NAME = "date_added";
}

Here is part of my DataBaseHandlar class:

public class DatabaseHandlar extends SQLiteOpenHelper {

private final Context context;

public DatabaseHandlar(@Nullable Context context) {
    super(context, Constants.DB_NAME, null, Constants.DB_VERSION);
    this.context = context;
}

@Override
public void onCreate(SQLiteDatabase db) {
    String CREATE_BABY_TABLE = "CREATE TABLE " + Constants.TABLE_NAME + "("
            + Constants.KEY_ID + " INTEGER PRIMARY KEY,"
            + Constants.KEY_BABY_ITEM + " INTEGER,"
            + Constants.KEY_COLOR + " TEXT,"
            + Constants.KEY_QTY_NUMBER + " INTEGER,"
            + Constants.KEY_ITEM_SIZE + " INTEGER,"
            + Constants.KEY_DATE_NAME + " LONG);";

    db.execSQL(CREATE_BABY_TABLE);

}

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

    db.execSQL("DROP TABLE IF EXISTS " + Constants.TABLE_NAME);

    onCreate(db);
}

// CRUD operations
public void addItem(Item item) {
    SQLiteDatabase db = this.getWritableDatabase();

    ContentValues values = new ContentValues();
    values.put(Constants.KEY_BABY_ITEM, item.getItemName());
    values.put(Constants.KEY_COLOR, item.getItemColor());
    values.put(Constants.KEY_QTY_NUMBER, item.getItemQuantity());
    values.put(Constants.KEY_ITEM_SIZE, item.getItemSize());
    values.put(Constants.KEY_DATE_NAME, java.lang.System.currentTimeMillis());//timestamp of the system

    //Inset the row
    db.insert(Constants.TABLE_NAME, null, values);

    Log.d("DBHandler", "added Item: ");
}

Answer 1

You can use the ALTER TABLE statement, this is used to add, delete, or modify columns in an existing table.

For example:

ALTER TABLE table_name
ADD column_name datatype;

Answer 2

ALTER TABLE is what you are looking for

ALTER TABLE {tableName} ADD COLUMN {columnName} {type};

Answer 3

You would need to manually alter the table with

if(oldVersion == 1 && newVersion ==2){
    try {
         db.execSQL("ALTER TABLE " + Constants.TABLE_NAME + " ADD COLUMN mobilenumber TEXT DEFAULT ''");
        } catch (Exception ignored) {
            recreateDb(db);
        }
} else {
    onCreate(db);
}

put that in the onUpgrade method