2、函數(shù)public void onCreate(SQLiteDatabase db)是在調(diào)用getReadableDatabase()或者是getWritableDatabase()第一次創(chuàng)立數(shù)據(jù)庫的時(shí)候執(zhí)行,實(shí)際上是在第一次失掉SQLiteDatabse對象的時(shí)候，才會(huì)調(diào)用這個(gè)方法.

public void onCreate(SQLiteDatabase db) { 
  System.out.println("create a Database"); 
  //execSQL函數(shù)用于執(zhí)行SQL語句 
  db.execSQL("create table user(id int,name varchar(20))"); 
}   

    private static DatabaseHelper mDbHelper;
    private static SQLiteDatabase mDb;

    private static final String   DATABASE_NAME    = "life";

    private static final int      DATABASE_VERSION = 1;

    private Context               mCtx;

    private static class DatabaseHelper extends SQLiteOpenHelper {

        DatabaseHelper(Context context) {
            super(context, DATABASE_NAME, null, DATABASE_VERSION);
        }

        @Override
        public void onCreate(SQLiteDatabase db) {
            //創(chuàng)立表結(jié)構(gòu)
            db.execSQL("CREATE TABLE life_history (id INTEGER PRIMARY KEY AUTOINCREMENT,type TEXT, city TEXT, company TEXT, pucNum TEXT, pucName TEXT);");
        }

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

    public DBHelper(Context ctx) throws SQLException {
        this.mCtx = ctx;
        mDbHelper = new DatabaseHelper(mCtx);
        mDb = mDbHelper.getWritableDatabase();
    }

    /**
     * 關(guān)閉數(shù)據(jù)源
     */
    public void closeConnection() {
        if (mDb != null && mDb.isOpen())
            mDb.close();
        if (mDbHelper != null)
            mDbHelper.close();
    }

    /**
     * 插入數(shù)據(jù) 參數(shù)
     * @param tableName 表名
     * @param initialValues 要插入的列對應(yīng)值
     * @return
     */
    public long insert(String tableName, ContentValues initialValues) {

        return mDb.insert(tableName, null, initialValues);
    }

    /**
     * 刪除數(shù)據(jù)
     * @param tableName 表名
     * @param deleteCondition 條件
     * @param deleteArgs 條件對應(yīng)的值（如果deleteCondition中有“？”號，將用此數(shù)組中的值替換，一一對應(yīng)）
     * @return
     */
    public boolean delete(String tableName, String deleteCondition, String[] deleteArgs) {

        return mDb.delete(tableName, deleteCondition, deleteArgs) > 0;
    }

    /**
     * 更新數(shù)據(jù)
     * @param tableName 表名
     * @param initialValues 要更新的列
     * @param selection 更新的條件
     * @param selectArgs 更新條件中的“？”對應(yīng)的值
     * @return
     */
    public boolean update(String tableName, ContentValues initialValues, String selection, String[] selectArgs) {
        return mDb.update(tableName, initialValues, selection, selectArgs) > 0;
    }

    /**
     * 取得一個(gè)列表
     * @param distinct 是否去重復(fù)
     * @param tableName 表名
     * @param columns 要返回的列
     * @param selection 條件
     * @param selectionArgs 條件中“？”的參數(shù)值
     * @param groupBy 分組
     * @param having 分組過濾條件
     * @param orderBy 排序
     * @return
     */
    public Cursor findList(boolean distinct, String tableName, String[] columns, String selection, String[] selectionArgs, String groupBy, String having, String orderBy, String limit) {

        return mDb.query(distinct, tableName, columns, selection, selectionArgs, groupBy, having, orderBy, limit);
    }

    /**
     * 取得單行記錄
     * @param tableName 表名
     * @param columns 獲取的列數(shù)組
     * @param selection 條件
     * @param selectionArgs 條件中“？”對應(yīng)的值
     * @param groupBy 分組
     * @param having 分組條件
     * @param orderBy 排序
     * @param limit 數(shù)據(jù)區(qū)間
     * @param distinct 是否去重復(fù)
     * @return
     * @throws SQLException
     */
    public Cursor findOne(boolean distinct, String tableName, String[] columns, String selection, String[] selectionArgs, String groupBy, String having, String orderBy, String limit) throws SQLException {

        Cursor mCursor = findList(distinct, tableName, columns, selection, selectionArgs, groupBy, having, orderBy, limit);

        if (mCursor != null) {
            mCursor.moveToFirst();
        }
        return mCursor;

    }

    /**
     * 執(zhí)行SQL(帶參數(shù))
     * @param sql
     * @param args SQL中“？”參數(shù)值
     */
    public void execSQL(String sql, Object[] args) {
        mDb.execSQL(sql, args);

    }

    /**
     * 執(zhí)行SQL
     * @param sql
     */
    public void execSQL(String sql) {
        mDb.execSQL(sql);

    }

    /**
     * 判斷某張表是否存在
     * @param tabName 表名
     * @return
     */
    public boolean isTableExist(String tableName) {
        boolean result = false;
        if (tableName == null) {
            return false;
        }

        try {
            Cursor cursor = null;
            String sql = "select count(1) as c from sqlite_master where type ='table' and name ='" + tableName.trim() + "'";
            cursor = mDb.rawQuery(sql, null);
            if (cursor.moveToNext()) {
                int count = cursor.getInt(0);
                if (count > 0) {
                    result = true;
                }
            }

            cursor.close();
        }
        catch (Exception e) {
        }
        return result;
    }

    /**
     * 判斷某張表中是否存在某字段(注，該方法無法判斷表是否存在，因此應(yīng)與isTableExist一起應(yīng)用)
     * @param tabName 表名
     * @param columnName 列名
     * @return
     */
    public boolean isColumnExist(String tableName, String columnName) {
        boolean result = false;
        if (tableName == null) {
            return false;
        }

        try {
            Cursor cursor = null;
            String sql = "select count(1) as c from sqlite_master where type ='table' and name ='" + tableName.trim() + "' and sql like '%" + columnName.trim() + "%'";
            cursor = mDb.rawQuery(sql, null);
            if (cursor.moveToNext()) {
                int count = cursor.getInt(0);
                if (count > 0) {
                    result = true;
                }
            }

            cursor.close();
        }
        catch (Exception e) {
        }
        return result;
    }

}