Question

所以我一直在尝试从SELECT方法保存结果而不返回任何内容。

我不确定我在做什么错。我将不胜感激！

此getData（）函数的输出为“”。一点都没有。

我的代码在下面：

public String getData(int firstSelection, int secondSelection, int thirdSelection,
                          int fourthSelection, int fifthSelection)
    {
        SQLiteDatabase db = dbHelper.getWritableDatabase();
        String firstSelectionStr, secondSelectionStr, thirdSelectionStr, fourthSelectionStr, fifthSelectionStr;

        firstSelectionStr = Integer.toString(firstSelection);
        secondSelectionStr = Integer.toString(secondSelection);
        thirdSelectionStr = Integer.toString(thirdSelection);
        fourthSelectionStr = Integer.toString(fourthSelection);
        fifthSelectionStr = Integer.toString(fifthSelection);

        String[] columns = {DBHelper.UID,DBHelper.CNAME};
        //Cursor cursor = db.query(DBHelper.TABLE_NAME,columns,null,null,null,null,null);
        String selectQuery = "SELECT " + DBHelper.CNAME + " FROM "+ DBHelper.TABLE_NAME + " WHERE First_Attribute=? "
                + " AND Second_Attribute=? " + " AND Third_Attribute=? " + " AND Fourth_Attribute=? "
                + " AND Fifth_Attribute=? ";
        Cursor cursor=db.rawQuery(selectQuery, new String[] {firstSelectionStr, secondSelectionStr, thirdSelectionStr,
                            fourthSelectionStr, fifthSelectionStr});
        StringBuilder buffer = new StringBuilder();

        // Append every data together
        while (cursor.moveToNext())
        {
            //int cursorID = cursor.getInt(cursor.getColumnIndex(DBHelper.UID));
            String chosenItem = cursor.getString(cursor.getColumnIndex(DBHelper.CNAME));
            buffer.append(chosenItem + "/n");
        }
        return buffer.toString();
    }

我的数据库模型也在下面。我有两张桌子。一种是用于收藏工艺品，TABLE_NAME，另一种是用于存放所选工艺品的RESULT_TABLE。

    static class DBHelper extends SQLiteOpenHelper
    {
        private static final String DATABASE_NAME = "CraftsAppDatabase.db";    // Database Name
        private static final String TABLE_NAME = "CraftTools";   // Table Name
        private static final String RESULT_TABLE = "Result";   // Table Name
        private static final int DATABASE_Version = 1;    // Database Version
        private static final String UID="_id";     // Column I (Primary Key)
        private static final String CNAME = "Craft_Name";    //Column II
        private static final String RESULT = "Result_Name";    //Column II
        private static final String FIRST_ATTRIBUTE = "First_Attribute";    //Column III
        private static final String SECOND_ATTRIBUTE = "Second_Attribute";    //Column IV
        private static final String THIRD_ATTRIBUTE = "Third_Attribute";    //Column V
        private static final String FOURTH_ATTRIBUTE = "Fourth_Attribute";    //Column VI
        private static final String FIFTH_ATTRIBUTE = "Fifth_Attribute";    //Column VII
        private static final String CREATE_TABLE = "CREATE TABLE "+TABLE_NAME+
                " ("+UID+" INTEGER PRIMARY KEY AUTOINCREMENT, "+CNAME+" VARCHAR(255)" +
                ", "+FIRST_ATTRIBUTE+" VARCHAR(255), "+SECOND_ATTRIBUTE+" VARCHAR(255)" +
                ", "+THIRD_ATTRIBUTE+" VARCHAR(255), "+FOURTH_ATTRIBUTE+" VARCHAR(255)" +
                ", "+FIFTH_ATTRIBUTE+" VARCHAR(255));";
        private static final String CREATE_OTHER_TABLE = "CREATE TABLE "+RESULT_TABLE+
                " ("+UID+" INTEGER PRIMARY KEY AUTOINCREMENT, "+RESULT+" VARCHAR(255));";
        private static final String DROP_TABLE ="DROP TABLE IF EXISTS "+RESULT_TABLE;
        private Context context;

        public DBHelper(Context context) {
            super(context, DATABASE_NAME, null, DATABASE_Version);
            this.context=context;
        }

        /*public void deleteTable(SQLiteDatabase db) {
            db = getWritableDatabase();
            db.execSQL("DROP TABLE IF EXISTS CraftTools");
        }*/

        public void onCreate(SQLiteDatabase db) {
            db.execSQL(DROP_TABLE);
            db.execSQL(CREATE_OTHER_TABLE);
            db.execSQL(CREATE_TABLE);
            db.execSQL("INSERT INTO " + TABLE_NAME + "(Craft_Name, First_Attribute, Second_Attribute, Third_Attribute, Fourth_Attribute, Fifth_Attribute ) " +
                    "VALUES ('Landscape Drawing', '1', '4','8', '0', '0')");
            db.execSQL("INSERT INTO " + TABLE_NAME + "(Craft_Name, First_Attribute, Second_Attribute, Third_Attribute, Fourth_Attribute, Fifth_Attribute ) " +
                    "VALUES ('Popsicle Sticks House', '2', '3','0', '0', '0')");
            db.execSQL("INSERT INTO " + TABLE_NAME + "(Craft_Name, First_Attribute, Second_Attribute, Third_Attribute, Fourth_Attribute, Fifth_Attribute ) " +
                    "VALUES ('Sunset Painting', '4', '7','10', '0', '0')");

        }

        @Override
        public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
            //db.execSQL(DROP_TABLE);
            onCreate(db);
            if (newVersion > oldVersion) {
                db.execSQL("ALTER TABLE CraftTools ADD COLUMN FIRST_ATTRIBUTE INTEGER DEFAULT 0");
                db.execSQL("ALTER TABLE CraftTools ADD COLUMN SECOND_ATTRIBUTE INTEGER DEFAULT 0");
                db.execSQL("ALTER TABLE CraftTools ADD COLUMN THIRD_ATTRIBUTE INTEGER DEFAULT 0");
                db.execSQL("ALTER TABLE CraftTools ADD COLUMN FOURTH_ATTRIBUTE INTEGER DEFAULT 0");
                db.execSQL("ALTER TABLE CraftTools ADD COLUMN FIFTH_ATTRIBUTE INTEGER DEFAULT 0");
            }
        }


    }
}

Answer 1

您的selectQuery字符串将建立一个SQL查询，该查询仅选择具有所有5个匹配的属性的值。

因此，如果您调用getData(1, 4, 8, 0, 0)或getData(2, 3, 0, 0, 0)或getData(4, 7, 10, 0, 0)，则将获得返回值，但是SQL不会选择任何内容，并且getData将不包含任何数据

Android Studio我的rawQuery或“ SELECT”未返回任何内容

1 个答案: