在Android中執行select語句

Question

我想創建一個新方法並捕獲所有值，並將它們作爲int返回。 db.execSQL表示它執行一個不返回數據的單個sql語句。 fehlzeiten是一個字符串，但它僅包括數字

public class NotesDbAdapter { 

public static final String KEY_TITLE = "title"; 
public static final String KEY_BODY = "body"; 
public static final String KEY_ROWID = "_id"; 
public static final String KEY_Test = "test"; 
public static final String KEY_Time = "fehlzeiten"; 
private static final String TAG = "NotesDbAdapter"; 
private DatabaseHelper mDbHelper; 
private SQLiteDatabase mDb; 

/** 
* Database creation sql statement 
*/ 

private static final String DATABASE_CREATE = 
    "create table notes (_id integer primary key autoincrement, " 
    + "title text not null, body text not null, fehlzeiten text not null, test text not null);"; 

private static final String DATABASE_NAME = "data"; 
private static final String DATABASE_TABLE = "notes"; 
private static final int DATABASE_VERSION = 4; 

private final Context mCtx; 

private static class DatabaseHelper extends SQLiteOpenHelper { 

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

    @Override 

    public void onCreate(SQLiteDatabase db) { 
     db.execSQL(DATABASE_CREATE); 

    } 

    @Override 
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) { 
     Log.w(TAG, "Upgrading database from version " + oldVersion + " to " 
       + newVersion + ", which will destroy all old data"); 
     db.execSQL("DROP TABLE IF EXISTS notes"); 
     onCreate(db); 
    } 
} 

/** 
* Constructor - takes the context to allow the database to be 
* opened/created 
* 
* @param ctx the Context within which to work 
*/ 
public NotesDbAdapter(Context ctx) { 
    this.mCtx = ctx; 
} 

/** 
* Open the notes database. If it cannot be opened, try to create a new 
* instance of the database. If it cannot be created, throw an exception to 
* signal the failure 
* 
* @return this (self reference, allowing this to be chained in an 
*   initialization call) 
* @throws SQLException if the database could be neither opened or created 
*/ 
public NotesDbAdapter open() throws SQLException { 
    mDbHelper = new DatabaseHelper(mCtx); 
    mDb = mDbHelper.getWritableDatabase(); 
    return this; 
} 

public void close() { 
    mDbHelper.close(); 
} 


/** 
* Create a new note using the title and body provided. If the note is 
* successfully created return the new rowId for that note, otherwise return 
* a -1 to indicate failure. 
* 
* @param title the title of the note 
* @param body the body of the note 
* @return rowId or -1 if failed 
*/ 
public long createNote(String title, String body, String fehlzeit, String test) { 
    ContentValues initialValues = new ContentValues(); 
    initialValues.put(KEY_TITLE, title); 
    initialValues.put(KEY_BODY, body); 
    initialValues.put(KEY_Time, fehlzeit); 
    initialValues.put(KEY_Test, test); 

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

/** 
* Delete the note with the given rowId 
* 
* @param rowId id of note to delete 
* @return true if deleted, false otherwise 
*/ 
public boolean deleteNote(long rowId) { 

    return mDb.delete(DATABASE_TABLE, KEY_ROWID + "=" + rowId, null) > 0; 
} 

/** 
* Return a Cursor over the list of all notes in the database 
* 
* @return Cursor over all notes 
*/ 
public Cursor fetchAllNotes() { 

    return mDb.query(DATABASE_TABLE, new String[] {KEY_ROWID, KEY_TITLE, 
      KEY_BODY,KEY_Time,KEY_Test}, null, null, null, null, null); 
} 




/** 
* Return a Cursor positioned at the note that matches the given rowId 
* 
* @param rowId id of note to retrieve 
* @return Cursor positioned to matching note, if found 
* @throws SQLException if note could not be found/retrieved 
*/ 
public Cursor fetchNote(long rowId) throws SQLException { 

    Cursor mCursor = 

     mDb.query(true, DATABASE_TABLE, new String[] {KEY_ROWID, 
       KEY_TITLE, KEY_BODY,KEY_Time,KEY_Test}, KEY_ROWID + "=" + rowId, null, 
       null, null, null, null); 
    if (mCursor != null) { 
     mCursor.moveToFirst(); 
    } 
    return mCursor; 

} 


/** 
* Update the note using the details provided. The note to be updated is 
* specified using the rowId, and it is altered to use the title and body 
* values passed in 
* 
* @param rowId id of note to update 
* @param title value to set note title to 
* @param body value to set note body to 
* @return true if the note was successfully updated, false otherwise 
*/ 
public boolean updateNote(long rowId, String title, String body, String fehlzeiten, String test) { 
    ContentValues args = new ContentValues(); 
    args.put(KEY_TITLE, title); 
    args.put(KEY_BODY, body); 
    args.put(KEY_Time, fehlzeiten); 
    args.put(KEY_Test, test); 

    return mDb.update(DATABASE_TABLE, args, KEY_ROWID + "=" + rowId, null) > 0; 
} 

private int ausgabe() 
{ 
    //i want to return the sum of all entrys in fehlzeit here 



} 

} 

也許它不是最好使用SQL，但我不知道我能做到，否則

Answer 1

您原始查詢應該是這樣的：

String rawQuery = 
    "SELECT _id, fehlzeiten, 
      SUM(fehlzeiten) as sum 
      FROM notes"; 

稍後在您的光標中，您將有一個名爲「sum」的列，它將保存您的值。

您需要SQLiteDatabase類型的對象，我們稱之爲sqliteDB。您執行查詢是這樣的：

sqliteCallLogsDB.rawQuery(rawQuery, null); 

如果你不熟悉基本操作，你應該走和閱讀tutorial，因爲這會爲你節省大量的時間和要求（並等待答案）方式。