Question

考虑我有一个包含两个表A和B的数据库。在某个时间我想检查表A是否已经在数据库中创建.. plz帮助我如何找到某个表是否存在在数据库？

提前致谢。

Answer 1

SELECT * FROM sqlite_master where type='table' and name='my_table_name'

Answer 2

您可以像这样发出SQL查询：

SELECT name FROM sqlite_master
WHERE type IN ('table','view') AND name NOT LIKE 'sqlite_%'
UNION ALL
SELECT name FROM sqlite_temp_master
WHERE type IN ('table','view')
ORDER BY 1

此表包含DB中所有表的列表。只需添加另一个名字。

Answer 3

public class DatabaseHelper extends SQLiteOpenHelper {

    private static String DB_PATH = "ur path";
    private static String DB_NAME = ur db name;
    private static SQLiteDatabase myDataBase;
    private static DatabaseHelper databaseHelper = null;

    private final Context myContext;

    private static boolean doCopyDatabase = true;

    private DatabaseHelper(Context context) {
        super(context, DB_NAME, null, 1);
        myContext = context.getApplicationContext();
    }

    /**
     * To check whether the databaseHelper and the database is existing or not.
     * If databaseHelper is existing, a function is called to open the database.
     * If there is no database, new database is created. If databaseHelper in
     * not existing, new databaseHelper is created.
     */
    public static DatabaseHelper getInstance(Context context) {
        if (databaseHelper == null) {

            databaseHelper = new DatabaseHelper(context.getApplicationContext());
            databaseHelper.openDataBase();
            if (myDataBase == null) {
                try {
                    myDataBase = databaseHelper.getWritableDatabase();
                    if (doCopyDatabase) {
                        databaseHelper.copyDataBase();
                    } else {
                        databaseHelper.runSchemaCreator();
                    }
                } catch (Exception e) {
                    Log.e("Exception in DatabaseHelper: getInstance()", e
                            .getMessage());
                }
                databaseHelper.openDataBase();
            }
        }
        return databaseHelper;
    }

    /**
     * @param doCopyDatabase the doCopyDatabase to set
     */
    public static void setDoCopyDatabase(boolean doCopyDatabase) {
        DatabaseHelper.doCopyDatabase = doCopyDatabase;
    }

    private void runSchemaCreator() {
        TablesCreator tablesCreator = new TablesCreator(myDataBase);
        try {
            tablesCreator.createTables();
        } catch (SQLiteException e) {
            Log.i("Error in DatabaseHelper : createTables()", e.getMessage());
        }
    }

    /**
     * Returns the database.
     */
    public SQLiteDatabase getDatabase() {
        return myDataBase;
    }

    /**
     * Opens the database.
     * 
     * @return
     * @throws SQLException
     */
    private boolean openDataBase() throws SQLException {
        String myPath = DB_PATH + DB_NAME;
        try {
            myDataBase = SQLiteDatabase.openDatabase(myPath, null,
                    SQLiteDatabase.OPEN_READWRITE);
        } catch (SQLiteException e) {
            Log.i("Exception in DatabaseHelper : openDatabase()", e
                    .getMessage());
        }
        return myDataBase != null ? true : false;
    }

    @Override
    public synchronized void close() {
        if (myDataBase != null) {
            myDataBase.close();
            myDataBase = null;
        }
        super.close();
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
    }

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

public class TablesCreator {

    private SQLiteDatabase myDataBase;

    public TablesCreator(SQLiteDatabase db) {
        this.myDataBase = db;
    }


    public void createTables() {    
    }
}

Answer 4

一个非常简单的解决方案。不确定它的可信度。在http://www.sqlite.org/sqlite.html查看sqlite3的特殊命令部分 .tables A是你发给sqlite的命令。在SQLiteDatabase类中使用rawQuery方法。如果没有帮助的话，Plz就不会这样做。

Cursor myCursor = mySQLiteDatabase.rawQuery(".tables A", null);
if(myCursor.moveToFirst()){
    //table exists
} else {
   //table does not exist
}

如何在android中查找数据库中存在的表？

4 个答案: