android - 通过方法创建具有连续编号的表

Question

我想建立一个 GPS 数据库，其中每个表代表一次旅行。为此，有必要通过按下按钮来创建一个新表。

到目前为止，我已经完成了一切。

但我希望表格按照这种模式显示:行程_1；行程_2； Trip_3 ...

但我总是收到表名为空的错误消息。

android.database.sqlite.SQLiteException: near "Table": syntax error (code 1): , while compiling: CREATE TABLE Trip_ (ID INTEGER PRIMARY KEY, Table TEXT)

请帮我找出我的错误。

这是我的数据库类:

public class GPSDatabase extends SQLiteOpenHelper {

String TAG = "GPSDatabase";

int tnumber = 0;


public static GPSDatabase INSTANCE = null;

private static final String DB_NAME              = "eelo";
private static final int    VERSION              = 1;
public  static       String TABLE_NAME           = "Trip_0";
public  static final String TABLE_TRIP           = "Trip_";

public  static final String TABLE_COLUMN         = "Table";

public  static final String ID_COLUMN            = "ID";
public  static final String NUMBER_COLUMN        = "Number";
public  static final String DISTANCE_COLUMN      = "Distance";
public  static final String LATITUDE_COLUMN      = "Latitude";
public  static final String LONGITUDE_COLUMN     = "Longitude";


private GPSDatabase(Context context) {
    super(context, DB_NAME, null, VERSION);
}


public static GPSDatabase getInstance (final Context context){
    if (INSTANCE == null){
        INSTANCE = new GPSDatabase(context);
    }
    return INSTANCE;
}

@Override
public void onCreate(SQLiteDatabase db) {


    String createTripQuery =
                "CREATE TABLE " + TABLE_TRIP + " (" + ID_COLUMN + " INTEGER PRIMARY KEY, " + TABLE_COLUMN + " TEXT)";

    String createQuery;
    if (tnumber==0) {
        createQuery =
                "CREATE TABLE " + TABLE_NAME + " (" + ID_COLUMN + " INTEGER PRIMARY KEY, " + NUMBER_COLUMN + " INTEGER DEFAULT NULL, " + DISTANCE_COLUMN + " INTEGER DEFAULT NULL, " + LATITUDE_COLUMN + " REAL DEFAULT NULL, " + LONGITUDE_COLUMN + " REAL DEFAULT NULL)";
    }
    else{
        createQuery =
                "CREATE TABLE " + getTrip(tnumber) + " (" + ID_COLUMN + " INTEGER PRIMARY KEY, " + NUMBER_COLUMN + " INTEGER DEFAULT NULL, " + DISTANCE_COLUMN + " INTEGER DEFAULT NULL, " + LATITUDE_COLUMN + " REAL DEFAULT NULL, " + LONGITUDE_COLUMN + " REAL DEFAULT NULL)";
    }
    db.execSQL(createTripQuery);
    db.execSQL(createQuery);
    Log.d(TAG, "Table created");
    tnumber++;

}

在这里我得到了新 Trip 的表名:

public String getTrip(final long id) {

    SQLiteDatabase db = this.getReadableDatabase();
    Cursor cursor = db.query(TABLE_TRIP, new String[]{ID_COLUMN, TABLE_COLUMN}, ID_COLUMN + " = ?", new String[]{String.valueOf(id)}, null, null, null);

    String table = null;

    if (cursor != null && cursor.getCount() > 0) {
        cursor.moveToFirst();

        table = cursor.getString(cursor.getColumnIndex(TABLE_COLUMN));

    }

    Log.d(TAG, "getTable: "+table);
    return table;
}

这是主 Activity 中的 ONCLICK 方法；

public static GPSDatabase db;
public static int tripNumber = 0;
public static boolean clicked=false;
int NAV = 0;

@Override
protected void onCreate(Bundle savedInstanceState) {

...

    db = GPSDatabase.getInstance(this);

...

    Button btn= (Button)findViewById(R.id.button3);
    btn.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            // TODO Auto-generated method stub
            Log.d("new Trip ","clicked");
            tripNumber++;

            long newID = -1;

            try{
                SQLiteDatabase database = db.getWritableDatabase();

                ContentValues values = new ContentValues();

                values.put(db.TABLE_COLUMN, "Trip_"+tripNumber);

                newID = database.insert(db.TABLE_TRIP, null, values);

            }catch (SQLiteException e){
                Log.e(TAG,"insert");
            }finally {
                Log.d(TAG,"TableTrip insert with ID " + newID);
            }

            SQLiteDatabase db1;
            db1 = db.getWritableDatabase();
            db.TABLE_NAME = db.TABLE_TRIP+tripNumber;
            String dropTable = "DROP TABLE IF EXISTS " + (db.TABLE_NAME+(tripNumber-1));
            db1.execSQL(dropTable);
            String createQuery =
                    "CREATE TABLE " + db.TABLE_NAME + " (" + db.ID_COLUMN + " INTEGER PRIMARY KEY, " + db.NUMBER_COLUMN + " INTEGER DEFAULT NULL, " + db.DISTANCE_COLUMN + " INTEGER DEFAULT NULL, " + db.LATITUDE_COLUMN + " REAL DEFAULT NULL, " + db.LONGITUDE_COLUMN + " REAL DEFAULT NULL)";


            db1.execSQL(createQuery);
        }
    });
}

Answer 1

问题在于在 public static final String TABLE_COLUMN = "Table"; 中将列命名为 Table；
。 SQLite 假设它遇到了关键字 TABLE，这在语法上是错误的。

如果你真的想要一个名为 Table 的列，这是可能的，你可以使用 public static final String TABLE_COLUMN = "'Table'";
。但是，这仍然可能存在问题和令人困惑。

您也可以使用 _yourcolumnname 来避免使用推荐的(但很少使用)

SQLite adds new keywords from time to time when it takes on new features. So to prevent your code from being broken by future enhancements, you should normally quote any identifier that is an English language word, even if you do not have to.[emphasis added]

更多信息请访问 SQLite Keywords

所以也许 public static final String TABLE_COLUMN = "_Table";

但是，也许更好的解决方案是应用规范化(减少数据库冗余)并使用一个包含一列的表来标识行程，而不是使用多个结构相同的表。

例如你可以使用:-

private static final String DB_NAME              = "eelo";
private static final int    VERSION              = 1;
public  static final String TABLE_TRIP           = "Trip_";

public  static final String ID_COLUMN            = "ID";
public  static final String NUMBER_COLUMN        = "Number";
public  static final String DISTANCE_COLUMN      = "Distance";
public  static final String LATITUDE_COLUMN      = "Latitude";
public  static final String LONGITUDE_COLUMN     = "Longitude";
public  static final String TRIP_COLUMN          = "Trip";

然后您只需要一个表创建语句，在 onCreate 方法中没有任何逻辑，例如可能是:-

@Override
public void onCreate(SQLiteDatabase db) {

    String createQuery =
                "CREATE TABLE " + TABLE_NAME + " (" + 
                    ID_COLUMN + " INTEGER PRIMARY KEY, " + 
                    NUMBER_COLUMN + " INTEGER DEFAULT NULL, " +
                    DISTANCE_COLUMN + " INTEGER DEFAULT NULL, " +
                    LATITUDE_COLUMN + " REAL DEFAULT NULL, " +
                    LONGITUDE_COLUMN + " REAL DEFAULT NULL +
                    TRIP_COLUMN + "INTEGER" +
                    )";
    }
    db.execSQL(createQuery);
    Log.d(TAG, "Table created");
}

然后您将不需要 getTrip 来交换表，而您只需使用 WHERE trip = respective_trip_as_int(注意 int 可能很长，所以很可能有足够的数字)来产生相同的最终结果。