/*
 * Copyright (c) 2010-2011, The MiCode Open Source Community (www.micode.net)
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *        http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package net.micode.notes.data;


import android.content.ContentValues;//就是用于保存一些数据（string boolean byte double float int long short ...）信息，这些信息可以被数据库操作时使用。
import android.content.Context;//加载和访问资源。（android中主要是这两个功能，但是这里具体不清楚）
import android.database.sqlite.SQLiteDatabase;//主要提供了对应于添加、删除、更新、查询的操作方法： insert()、delete()、update()和query()。配合content.values
import android.database.sqlite.SQLiteOpenHelper;//用来管理数据的创建和版本更新
import android.util.Log;


import net.micode.notes.data.Notes.DataColumns;
import net.micode.notes.data.Notes.DataConstants;
import net.micode.notes.data.Notes.NoteColumns;
/*
* 功能描述：数据库操作，用SQLOpenhelper,对一些note和文件进行数据库的操作
*/

public class NotesDatabaseHelper extends SQLiteOpenHelper {
    private static final String DB_NAME = "note.db";// 数据库名

    private static final int DB_VERSION = 4;// 版本号

    public interface TABLE {
        /*
        * 接口，分成note和data,用于表示数据库中两种表格
        * */
        public static final String NOTE = "note";

        public static final String DATA = "data";
    }

    private static final String TAG = "NotesDatabaseHelper";// 日志标签，用于在日志中标识数据库操作的相关信息

    /*
    * NotesDatabaseHelper 类的实例，用于单例模式的数据库操作，通过 getInstance() 方法获取 NotesDatabaseHelper 的唯一实例
    * 单例模式是一种设计模式，在数据库操作中使用单例模式可以确保只有一个数据库连接，避免了重复创建和关闭数据库连接可能导致的性能问题
    */
    private static NotesDatabaseHelper mInstance;

    /*
    * 创建TABLE.NOTE表格，用于存储便签的相关信息
    */
    private static final String CREATE_NOTE_TABLE_SQL =
        "CREATE TABLE " + TABLE.NOTE + "(" +
            NoteColumns.ID + " INTEGER PRIMARY KEY," +// 便签ID
            NoteColumns.PARENT_ID + " INTEGER NOT NULL DEFAULT 0," +// 便签父级的ID
            NoteColumns.ALERTED_DATE + " INTEGER NOT NULL DEFAULT 0," +// 便签的提醒日期
            NoteColumns.BG_COLOR_ID + " INTEGER NOT NULL DEFAULT 0," + // 便签的背景颜色ID
            NoteColumns.CREATED_DATE + " INTEGER NOT NULL DEFAULT (strftime('%s','now') * 1000)," + // 便签的创建日期
            NoteColumns.HAS_ATTACHMENT + " INTEGER NOT NULL DEFAULT 0," +// 便签是否有附件
            NoteColumns.MODIFIED_DATE + " INTEGER NOT NULL DEFAULT (strftime('%s','now') * 1000)," +// 便签的最后修改日期
            NoteColumns.NOTES_COUNT + " INTEGER NOT NULL DEFAULT 0," +// 文件夹中的便签数量
            NoteColumns.SNIPPET + " TEXT NOT NULL DEFAULT ''," +// 文件夹名称或便签的文本内容
            NoteColumns.TYPE + " INTEGER NOT NULL DEFAULT 0," +// 便签的类型
            NoteColumns.WIDGET_ID + " INTEGER NOT NULL DEFAULT 0," +// 便签的Widget ID
            NoteColumns.WIDGET_TYPE + " INTEGER NOT NULL DEFAULT -1," +// 便签的Widget类型
            NoteColumns.SYNC_ID + " INTEGER NOT NULL DEFAULT 0," +// 便签的同步ID
            NoteColumns.LOCAL_MODIFIED + " INTEGER NOT NULL DEFAULT 0," +// 便签的本地修改标记
            NoteColumns.ORIGIN_PARENT_ID + " INTEGER NOT NULL DEFAULT 0," +// 原始父级便签的ID
            NoteColumns.GTASK_ID + " TEXT NOT NULL DEFAULT ''," +// 便签在Google任务中的ID
            NoteColumns.VERSION + " INTEGER NOT NULL DEFAULT 0" +// 便签的版本号
        ")";

    /*
    * 创建TABLE.DATA表格，用于存储便签中的数据
    */
    private static final String CREATE_DATA_TABLE_SQL =
        "CREATE TABLE " + TABLE.DATA + "(" +
            DataColumns.ID + " INTEGER PRIMARY KEY," +// 数据ID
            DataColumns.MIME_TYPE + " TEXT NOT NULL," +// 数据ID数据的MIME类型
            DataColumns.NOTE_ID + " INTEGER NOT NULL DEFAULT 0," +// 数据所属的便签的ID
            NoteColumns.CREATED_DATE + " INTEGER NOT NULL DEFAULT (strftime('%s','now') * 1000)," +// 数据的创建日期
            NoteColumns.MODIFIED_DATE + " INTEGER NOT NULL DEFAULT (strftime('%s','now') * 1000)," +// 数据的最后修改日期
            DataColumns.CONTENT + " TEXT NOT NULL DEFAULT ''," +// 数据的内容
            DataColumns.DATA1 + " INTEGER," +// 数据的附加信息1
            DataColumns.DATA2 + " INTEGER," +// 数据的附加信息2
            DataColumns.DATA3 + " TEXT NOT NULL DEFAULT ''," +// 数据的附加信息3
            DataColumns.DATA4 + " TEXT NOT NULL DEFAULT ''," +// 数据的附加信息4
            DataColumns.DATA5 + " TEXT NOT NULL DEFAULT ''" +// 数据的附加信息5
        ")";

    /*
     * 创建一个名为 note_id_index 的索引，在 TABLE.DATA 表格的 DataColumns.NOTE_ID 列上创建索引，以提高查询性能
     */
    private static final String CREATE_DATA_NOTE_ID_INDEX_SQL =
        "CREATE INDEX IF NOT EXISTS note_id_index ON " +
        TABLE.DATA + "(" + DataColumns.NOTE_ID + ");";

    /**
     * Increase folder's note count when move note to the folder
     */

    /*
    * 在更新 TABLE.NOTE 表格的 NoteColumns.PARENT_ID 列时，增加相应文件夹的便签计数
    * 通过更新 TABLE.NOTE 表格中的 NoteColumns.NOTES_COUNT 列，将其加1
     */
    private static final String NOTE_INCREASE_FOLDER_COUNT_ON_UPDATE_TRIGGER =
        "CREATE TRIGGER increase_folder_count_on_update "+
        " AFTER UPDATE OF " + NoteColumns.PARENT_ID + " ON " + TABLE.NOTE +
        " BEGIN " +
        "  UPDATE " + TABLE.NOTE +
        "   SET " + NoteColumns.NOTES_COUNT + "=" + NoteColumns.NOTES_COUNT + " + 1" +
        "  WHERE " + NoteColumns.ID + "=new." + NoteColumns.PARENT_ID + ";" +
        " END";

    /**
     * Decrease folder's note count when move note from folder
     */

    /*
    * 在更新 TABLE.NOTE 表格的 NoteColumns.PARENT_ID 列时，减少相应文件夹的便签计数
    * 通过更新 TABLE.NOTE 表格中的 NoteColumns.NOTES_COUNT 列，将其减1
    */
    private static final String NOTE_DECREASE_FOLDER_COUNT_ON_UPDATE_TRIGGER =
        "CREATE TRIGGER decrease_folder_count_on_update " +
        " AFTER UPDATE OF " + NoteColumns.PARENT_ID + " ON " + TABLE.NOTE +
        " BEGIN " +
        "  UPDATE " + TABLE.NOTE +
        "   SET " + NoteColumns.NOTES_COUNT + "=" + NoteColumns.NOTES_COUNT + "-1" +
        "  WHERE " + NoteColumns.ID + "=old." + NoteColumns.PARENT_ID +
        "  AND " + NoteColumns.NOTES_COUNT + ">0" + ";" +
        " END";

    /**
     * Increase folder's note count when insert new note to the folder
     */

    /*
    * 在向 TABLE.NOTE 表格插入新便签时，增加相应文件夹的便签计数
    * 通过更新 TABLE.NOTE 表格中的 NoteColumns.NOTES_COUNT 列，将其加1
    */
    private static final String NOTE_INCREASE_FOLDER_COUNT_ON_INSERT_TRIGGER =
        "CREATE TRIGGER increase_folder_count_on_insert " +
        " AFTER INSERT ON " + TABLE.NOTE +
        " BEGIN " +
        "  UPDATE " + TABLE.NOTE +
        "   SET " + NoteColumns.NOTES_COUNT + "=" + NoteColumns.NOTES_COUNT + " + 1" +
        "  WHERE " + NoteColumns.ID + "=new." + NoteColumns.PARENT_ID + ";" +
        " END";

    /**
     * Decrease folder's note count when delete note from the folder
     */

    /*
    * 在从 TABLE.NOTE 表格删除便签时，减少相应文件夹的便签计数
    * 通过更新 TABLE.NOTE 表格中的 NoteColumns.NOTES_COUNT 列，将其减1
    */
    private static final String NOTE_DECREASE_FOLDER_COUNT_ON_DELETE_TRIGGER =
        "CREATE TRIGGER decrease_folder_count_on_delete " +
        " AFTER DELETE ON " + TABLE.NOTE +
        " BEGIN " +
        "  UPDATE " + TABLE.NOTE +
        "   SET " + NoteColumns.NOTES_COUNT + "=" + NoteColumns.NOTES_COUNT + "-1" +
        "  WHERE " + NoteColumns.ID + "=old." + NoteColumns.PARENT_ID +
        "  AND " + NoteColumns.NOTES_COUNT + ">0;" +
        " END";

    /**
     * Update note's content when insert data with type {@link DataConstants#NOTE}
     */

    /*
    * 在向 TABLE.DATA 表格插入类型为 DataConstants.NOTE 的数据时，更新对应便签的内容
    * 通过更新 TABLE.NOTE 表格中的 NoteColumns.SNIPPET 列，将其设置为新插入数据的内容
    */
    private static final String DATA_UPDATE_NOTE_CONTENT_ON_INSERT_TRIGGER =
        "CREATE TRIGGER update_note_content_on_insert " +
        " AFTER INSERT ON " + TABLE.DATA +
        " WHEN new." + DataColumns.MIME_TYPE + "='" + DataConstants.NOTE + "'" +
        " BEGIN" +
        "  UPDATE " + TABLE.NOTE +
        "   SET " + NoteColumns.SNIPPET + "=new." + DataColumns.CONTENT +
        "  WHERE " + NoteColumns.ID + "=new." + DataColumns.NOTE_ID + ";" +
        " END";

    /**
     * Update note's content when data with {@link DataConstants#NOTE} type has changed
     */

    /*
    * 在更新类型为 DataConstants.NOTE 的数据时，更新对应便签的内容
    * 通过触发器在 TABLE.DATA 表格上创建，在数据被更新后将新的内容更新到对应的便签中
    */
    private static final String DATA_UPDATE_NOTE_CONTENT_ON_UPDATE_TRIGGER =
        "CREATE TRIGGER update_note_content_on_update " +
        " AFTER UPDATE ON " + TABLE.DATA +
        " WHEN old." + DataColumns.MIME_TYPE + "='" + DataConstants.NOTE + "'" +
        " BEGIN" +
        "  UPDATE " + TABLE.NOTE +
        "   SET " + NoteColumns.SNIPPET + "=new." + DataColumns.CONTENT +
        "  WHERE " + NoteColumns.ID + "=new." + DataColumns.NOTE_ID + ";" +
        " END";

    /**
     * Update note's content when data with {@link DataConstants#NOTE} type has deleted
     */

    /*
     * 在删除类型为 DataConstants.NOTE 的数据时，更新对应便签的内容
     * 通过触发器在 TABLE.DATA 表格上创建，在数据被删除后将对应的便签内容清空
     */
    private static final String DATA_UPDATE_NOTE_CONTENT_ON_DELETE_TRIGGER =
        "CREATE TRIGGER update_note_content_on_delete " +
        " AFTER delete ON " + TABLE.DATA +
        " WHEN old." + DataColumns.MIME_TYPE + "='" + DataConstants.NOTE + "'" +
        " BEGIN" +
        "  UPDATE " + TABLE.NOTE +
        "   SET " + NoteColumns.SNIPPET + "=''" +
        "  WHERE " + NoteColumns.ID + "=old." + DataColumns.NOTE_ID + ";" +
        " END";

    /**
     * Delete datas belong to note which has been deleted
     */

    /*
    * 在删除便签时，同时删除该便签相关的数据
    * 通过触发器在 TABLE.NOTE 表格上创建，在便签被删除后将与该便签相关的数据一并删除
    */
    private static final String NOTE_DELETE_DATA_ON_DELETE_TRIGGER =
        "CREATE TRIGGER delete_data_on_delete " +
        " AFTER DELETE ON " + TABLE.NOTE +
        " BEGIN" +
        "  DELETE FROM " + TABLE.DATA +
        "   WHERE " + DataColumns.NOTE_ID + "=old." + NoteColumns.ID + ";" +
        " END";

    /**
     * Delete notes belong to folder which has been deleted
     */

    /*
     * 在删除文件夹时，同时删除该文件夹下的所有便签
     * 通过触发器在 TABLE.NOTE 表格上创建，在文件夹被删除后将该文件夹下的所有便签一并删除。
     */
    private static final String FOLDER_DELETE_NOTES_ON_DELETE_TRIGGER =
        "CREATE TRIGGER folder_delete_notes_on_delete " +
        " AFTER DELETE ON " + TABLE.NOTE +
        " BEGIN" +
        "  DELETE FROM " + TABLE.NOTE +
        "   WHERE " + NoteColumns.PARENT_ID + "=old." + NoteColumns.ID + ";" +
        " END";

    /**
     * Move notes belong to folder which has been moved to trash folder
     */

    /*
     * 在将文件夹移动到回收站时，同时将该文件夹下的所有便签一并移动到回收站
     * 通过触发器在 TABLE.NOTE 表格上创建，在文件夹被移动到回收站后将该文件夹下的所有便签的父文件夹ID更新为回收站的ID
     */
    private static final String FOLDER_MOVE_NOTES_ON_TRASH_TRIGGER =
        "CREATE TRIGGER folder_move_notes_on_trash " +
        " AFTER UPDATE ON " + TABLE.NOTE +
        " WHEN new." + NoteColumns.PARENT_ID + "=" + Notes.ID_TRASH_FOLER +
        " BEGIN" +
        "  UPDATE " + TABLE.NOTE +
        "   SET " + NoteColumns.PARENT_ID + "=" + Notes.ID_TRASH_FOLER +
        "  WHERE " + NoteColumns.PARENT_ID + "=old." + NoteColumns.ID + ";" +
        " END";

    /*
    * 构造函数，传入数据库的名称和版本
    */
    public NotesDatabaseHelper(Context context) {
        super(context, DB_NAME, null, DB_VERSION);
    }

    /*
    * 用于创建存储标签属性的表格
    */
    public void createNoteTable(SQLiteDatabase db) {
        db.execSQL(CREATE_NOTE_TABLE_SQL);
        reCreateNoteTableTriggers(db);
        createSystemFolder(db);
        Log.d(TAG, "note table has been created");
    }

    /*
    * 用于重新创建数据库中的触发器
    */
    private void reCreateNoteTableTriggers(SQLiteDatabase db) {
        // 通过执行SQL语句DROP TRIGGER IF EXISTS来删除已存在的触发器，以确保不会重复创建
        db.execSQL("DROP TRIGGER IF EXISTS increase_folder_count_on_update");
        db.execSQL("DROP TRIGGER IF EXISTS decrease_folder_count_on_update");
        db.execSQL("DROP TRIGGER IF EXISTS decrease_folder_count_on_delete");
        db.execSQL("DROP TRIGGER IF EXISTS delete_data_on_delete");
        db.execSQL("DROP TRIGGER IF EXISTS increase_folder_count_on_insert");
        db.execSQL("DROP TRIGGER IF EXISTS folder_delete_notes_on_delete");
        db.execSQL("DROP TRIGGER IF EXISTS folder_move_notes_on_trash");
        // 创建新的触发器
        db.execSQL(NOTE_INCREASE_FOLDER_COUNT_ON_UPDATE_TRIGGER);// 增加文件夹计数的触发器
        db.execSQL(NOTE_DECREASE_FOLDER_COUNT_ON_UPDATE_TRIGGER);// 减少文件夹计数的触发器
        db.execSQL(NOTE_DECREASE_FOLDER_COUNT_ON_DELETE_TRIGGER);// 删除文件夹计数的触发器
        db.execSQL(NOTE_DELETE_DATA_ON_DELETE_TRIGGER);// 在删除时同时删除数据的触发器
        db.execSQL(NOTE_INCREASE_FOLDER_COUNT_ON_INSERT_TRIGGER);// 增加文件夹计数的触发器
        db.execSQL(FOLDER_DELETE_NOTES_ON_DELETE_TRIGGER);// 在删除时同时删除文件夹中的笔记的触发器
        db.execSQL(FOLDER_MOVE_NOTES_ON_TRASH_TRIGGER);// 将笔记移动到垃圾箱的触发器
    }

    /*
    *用于创建系统文件夹，插入四个不同类型的文件夹记录到 NoteColumns 表中
    */
    private void createSystemFolder(SQLiteDatabase db) {
        ContentValues values = new ContentValues();

        /**
         * call record foler for call notes
         */
        /*
         * 创建通话记录文件夹
         */
        values.put(NoteColumns.ID, Notes.ID_CALL_RECORD_FOLDER);
        values.put(NoteColumns.TYPE, Notes.TYPE_SYSTEM);
        db.insert(TABLE.NOTE, null, values);

        /**
         * root folder which is default folder
         */
        /*
         * 根目录，即默认文件夹
         */
        values.clear();
        values.put(NoteColumns.ID, Notes.ID_ROOT_FOLDER);
        values.put(NoteColumns.TYPE, Notes.TYPE_SYSTEM);
        db.insert(TABLE.NOTE, null, values);

        /**
         * temporary folder which is used for moving note
         */
        /*
         * 临时目录，用于移动笔记
         */
        values.clear();
        values.put(NoteColumns.ID, Notes.ID_TEMPARAY_FOLDER);
        values.put(NoteColumns.TYPE, Notes.TYPE_SYSTEM);
        db.insert(TABLE.NOTE, null, values);

        /**
         * create trash folder
         */
        /*
         * 创建垃圾箱
         */
        values.clear();
        values.put(NoteColumns.ID, Notes.ID_TRASH_FOLER);
        values.put(NoteColumns.TYPE, Notes.TYPE_SYSTEM);
        db.insert(TABLE.NOTE, null, values);
    }

    /*
     * 用于创建存储标签内容的表格
     */
    public void createDataTable(SQLiteDatabase db) {
        db.execSQL(CREATE_DATA_TABLE_SQL);// 执行 CREATE_DATA_TABLE_SQL 的 SQL 语句来创建数据表
        reCreateDataTableTriggers(db);// 调用 reCreateDataTableTriggers() 方法重新创建数据表中的触发器
        db.execSQL(CREATE_DATA_NOTE_ID_INDEX_SQL);// 执行 CREATE_DATA_NOTE_ID_INDEX_SQL 的 SQL 语句来创建一个索引
        Log.d(TAG, "data table has been created");
    }

    /*
    * 用于重新创建数据表中的触发器
    */
    private void reCreateDataTableTriggers(SQLiteDatabase db) {
        db.execSQL("DROP TRIGGER IF EXISTS update_note_content_on_insert");
        db.execSQL("DROP TRIGGER IF EXISTS update_note_content_on_update");
        db.execSQL("DROP TRIGGER IF EXISTS update_note_content_on_delete");

        db.execSQL(DATA_UPDATE_NOTE_CONTENT_ON_INSERT_TRIGGER);
        db.execSQL(DATA_UPDATE_NOTE_CONTENT_ON_UPDATE_TRIGGER);
        db.execSQL(DATA_UPDATE_NOTE_CONTENT_ON_DELETE_TRIGGER);
    }

    /*
    * 用于获取单例的数据库帮助类对象
    * 解决同一时刻只能有一个线程执行.
    * 在写程序库代码时，有时有一个类需要被所的其它类使用
    * 但又要求这个类只能被实例化一次，是个服务类，定义一次，其它类使用同一个这个类的实例
    */
    static synchronized NotesDatabaseHelper getInstance(Context context) {
        if (mInstance == null) {
            mInstance = new NotesDatabaseHelper(context);
        }
        return mInstance;
    }

    @Override
    /*
    * 在数据库第一次创建时被调用，用于创建所需的表格和触发器
    */
    public void onCreate(SQLiteDatabase db) {
        createNoteTable(db);
        createDataTable(db);
    }

    @Override
    /*
    * 根据旧版本和新版本之间的差异来执行相应的数据库升级操作
    */
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        boolean reCreateTriggers = false;
        boolean skipV2 = false;// 是否进行V2升级
        /*
        * 如果旧版本为1，则调用upgradeToV2方法
        */
        if (oldVersion == 1) {
            upgradeToV2(db);
            skipV2 = true; // this upgrade including the upgrade from v2 to v3
            oldVersion++;
        }
        /*
        * 如果旧版本为2且未跳过V2升级，则调用upgradeToV3方法
        */
        if (oldVersion == 2 && !skipV2) {
            upgradeToV3(db);
            reCreateTriggers = true;
            oldVersion++;
        }
        /*
        * 如果旧版本为3，则调用upgradeToV4方法
        */
        if (oldVersion == 3) {
            upgradeToV4(db);
            oldVersion++;
        }
        /*
        * 如果需要重新创建触发器，则调用reCreateNoteTableTriggers和reCreateDataTableTriggers方法重新创建触发器
        */
        if (reCreateTriggers) {
            reCreateNoteTableTriggers(db);
            reCreateDataTableTriggers(db);
        }
        /*
        * 如果旧版本和新版本不匹配，则抛出异常
        */
        if (oldVersion != newVersion) {
            throw new IllegalStateException("Upgrade notes database to version " + newVersion
                    + "fails");
        }
    }

    /*
    * 更新到V2版本
    * */
    private void upgradeToV2(SQLiteDatabase db) {
        /*
        * 通过执行SQL语句DROP TABLE IF EXISTS来删除旧的NOTE和DATA表格
        * */
        db.execSQL("DROP TABLE IF EXISTS " + TABLE.NOTE);
        db.execSQL("DROP TABLE IF EXISTS " + TABLE.DATA);
        createNoteTable(db);// 调用createNoteTable和createDataTable方法来创建新的NOTE表格
        createDataTable(db);// 调用createNoteTable和createDataTable方法来创建新的DATA表格
    }

    /*
    * 更新到V3版本
    * */
    private void upgradeToV3(SQLiteDatabase db) {
        /*
        * 执行SQL语句DROP TRIGGER IF EXISTS来移除不再使用的触发器
        * */
        // drop unused triggers
        db.execSQL("DROP TRIGGER IF EXISTS update_note_modified_date_on_insert");
        db.execSQL("DROP TRIGGER IF EXISTS update_note_modified_date_on_delete");
        db.execSQL("DROP TRIGGER IF EXISTS update_note_modified_date_on_update");
        /*
        * 执行ALTER TABLE语句向NOTE表格中添加一个新的列GTASK_ID，该列的类型是TEXT，并设置默认值为''
        * */
        // add a column for gtask id
        db.execSQL("ALTER TABLE " + TABLE.NOTE + " ADD COLUMN " + NoteColumns.GTASK_ID
                + " TEXT NOT NULL DEFAULT ''");
        /*
        * 通过ContentValues对象向NOTE表格中插入一条记录，该记录代表垃圾箱系统文件夹
        * */
        // add a trash system folder
        ContentValues values = new ContentValues();
        values.put(NoteColumns.ID, Notes.ID_TRASH_FOLER);
        values.put(NoteColumns.TYPE, Notes.TYPE_SYSTEM);
        db.insert(TABLE.NOTE, null, values);
    }

    /*
    * 更新到V4版本
    * */
    private void upgradeToV4(SQLiteDatabase db) {
        db.execSQL("ALTER TABLE " + TABLE.NOTE + " ADD COLUMN " + NoteColumns.VERSION
                + " INTEGER NOT NULL DEFAULT 0");// 通过执行ALTER TABLE语句向NOTE表格中添加一个新的列VERSION，该列的类型是INTEGER，并设置默认值为0
    }
}
