[英]Trouble using INNER JOIN in SQLite in Android
我在本地服務器上有一個MySQL數據庫。 我通過HTTP使用PHP和JSON從MySQL數據庫中獲取數據。 在Android應用中,使用JSON結果填充SQLite數據庫。 我已經驗證了SQLite數據庫實際上是通過運行類似於以下內容的測試查詢來填充的
Cursor cursor = database.rawQuery("SELECT recipe_id, ingredient_id, name FROM mm_ingredient_in_recipe_groups", null);
然后迭代結果光標以查看數據是否存在。 存在的數據存儲在三個表中:
mm_ingredients
,包含食譜的成分。 mm_recipes
,包含配方數據。 mm_ingredient_in_recipe
,包含用於將數據mm_recipes
和mm_ingredients
的數據(即解決多對多關系)。 我想做的是運行一個查詢,為參數配方名稱選擇成分。 這意味着我必須使用mm_ingredient_in_recipe
和mm_ingredients
來內mm_ingredient_in_recipe
mm_recipes
。
我嘗試運行以下查詢:
database.rawQuery("SELECT ingredient.name, ingredient.base_unit FROM mm_ingredients AS ingredient INNER JOIN mm_ingredient_in_recipe AS ir ON ir.ingredient_id = ingredient._id INNER JOIN mm_recipes AS recipe ON ir.recipe_id = recipe._id WHERE recipe.name = ?", new String[] {"Spicy tomatsuppe"});
這將返回一個空游標。 但是,在我的MySQL數據庫中,運行相應的查詢
SELECT ingredient.name, ingredient.base_unit FROM mm_ingredients AS ingredient INNER JOIN mm_ingredient_in_recipe AS ir ON ir.ingredient_id = ingredient.id INNER JOIN mm_recipes AS recipe ON ir.recipe_id = recipe.id WHERE recipe.name = "Spicy tomatsuppe";
返回期望的數據。 我在這里做錯了什么? 似乎我運行的每個查詢都可以正常工作,直到我開始包含INNER JOIN為止。 (據我所知,最好的做法是在SQLite中將id字段命名為_id。)
編輯:添加用於寫入數據庫的代碼:
以下是如何為表mm_recipes
填充數據庫的mm_recipes
。 其他兩個表也是如此。 我將JSONArray.optString()
用於SQLite的TEXT
數據類型,將JSONArray.optInt()
用於INTEGER
,將JSONArray.optDouble()
用於REAL
。
public static final String TABLE_NAME = "mm_recipes";
public static final String TABLE_NAME_IN_JSON = "mm_recipes";
public static final String COLUMN_ID = "_id";
public static final String COLUMN_NAME = "name";
public static final String COLUMN_IN_APP = "in_app";
public static final String COLUMN_DIFFICULTY = "difficulty";
public static final String COLUMN_TIME_CONSUMPTION_UPPER = "time_consumption_upper";
public static final String COLUMN_TIME_CONSUMPTION_LOWER = "time_consumption_lower";
public static final String COLUMN_PREPARATION_TIME = "preparation_time";
public static final String COLUMN_PORTIONS = "portions";
public static final String COLUMN_PORTIONS_UNIT = "portions_unit";
public static final String COLUMN_DESCRIPTION = "description";
public static final String COLUMN_TIPS = "tips";
public static final String COLUMN_USE_INGREDIENT_GROUPS = "use_ingredient_groups";
public static final void populateDatabase(SQLiteDatabase database, JSONObject databaseData) throws JSONException{
JSONArray table_data = databaseData.optJSONArray(TABLE_NAME_IN_JSON);
ContentValues contentValues = new ContentValues();
for (int i = 0; i < table_data.length(); i++){
JSONObject data = table_data.getJSONObject(i);
contentValues.clear();
contentValues.put(COLUMN_NAME, data.optString(COLUMN_NAME));
contentValues.put(COLUMN_IN_APP, data.optInt(COLUMN_IN_APP));
contentValues.put(COLUMN_DIFFICULTY, data.optString(COLUMN_DIFFICULTY));
contentValues.put(COLUMN_TIME_CONSUMPTION_UPPER, data.optInt(COLUMN_TIME_CONSUMPTION_UPPER));
contentValues.put(COLUMN_TIME_CONSUMPTION_LOWER, data.optInt(COLUMN_TIME_CONSUMPTION_LOWER));
contentValues.put(COLUMN_PREPARATION_TIME, data.optInt(COLUMN_PREPARATION_TIME));
contentValues.put(COLUMN_PORTIONS, data.optInt(COLUMN_PORTIONS));
contentValues.put(COLUMN_PORTIONS_UNIT, data.optString(COLUMN_PORTIONS_UNIT));
contentValues.put(COLUMN_DESCRIPTION, data.optString(COLUMN_DESCRIPTION));
contentValues.put(COLUMN_TIPS, data.optString(COLUMN_TIPS));
contentValues.put(COLUMN_USE_INGREDIENT_GROUPS, data.optInt(COLUMN_USE_INGREDIENT_GROUPS));
database.insert(TABLE_NAME, null, contentValues);
}
}
作為參考,這也是如何創建mm_recipe
表的示例。 在我的mm_recipe
類別中:
public static final String DATATYPE_ID = "INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL";
public static final String DATATYPE_NAME = "TEXT NOT NULL";
public static final String DATATYPE_IN_APP = "INTEGER DEFAULT 0";
public static final String DATATYPE_DIFFICULTY = "TEXT NOT NULL";
public static final String DATATYPE_TIME_CONSUMPTION_UPPER = "INTEGER NOT NULL";
public static final String DATATYPE_TIME_CONSUMPTION_LOWER = "INTEGER NOT NULL";
public static final String DATATYPE_PREPARATION_TIME = "INTEGER";
public static final String DATATYPE_PORTIONS = "INTEGER NOT NULL";
public static final String DATATYPE_PORTIONS_UNIT = "TEXT NOT NULL";
public static final String DATATYPE_DESCRIPTION = "TEXT";
public static final String DATATYPE_TIPS = "TEXT";
public static final String DATATYPE_USE_INGREDIENT_GROUPS = "INT";
/**Create table statement.*/
public static final String CREATE_TABLE =
"CREATE TABLE" + " " + TABLE_NAME + " (" +
COLUMN_ID + " " + DATATYPE_ID + ", " +
COLUMN_NAME + " " + DATATYPE_NAME + ", " +
COLUMN_IN_APP + " " + DATATYPE_IN_APP + ", " +
COLUMN_DIFFICULTY + " " + DATATYPE_DIFFICULTY + ", " +
COLUMN_TIME_CONSUMPTION_UPPER + " " + DATATYPE_TIME_CONSUMPTION_UPPER + ", " +
COLUMN_TIME_CONSUMPTION_LOWER + " " + DATATYPE_TIME_CONSUMPTION_LOWER + ", " +
COLUMN_PREPARATION_TIME + " " + DATATYPE_PREPARATION_TIME + ", " +
COLUMN_PORTIONS + " " + DATATYPE_PORTIONS + ", " +
COLUMN_PORTIONS_UNIT + " " + DATATYPE_PORTIONS_UNIT + ", " +
COLUMN_DESCRIPTION + " " + DATATYPE_DESCRIPTION + ", " +
COLUMN_TIPS + " " + DATATYPE_TIPS + ", " +
COLUMN_USE_INGREDIENT_GROUPS + " " + DATATYPE_USE_INGREDIENT_GROUPS + ");";
在我的SQLiteOpenHelper
類中:
@Override
public void onCreate(SQLiteDatabase database) {
database.execSQL(Table_mm_recipes.CREATE_TABLE);
database.execSQL(Table_mm_ingredient_in_recipe.CREATE_TABLE);
database.execSQL(Table_mm_ingredients.CREATE_TABLE);
}
事實證明,這是(很出乎意料的)一些愚蠢的錯誤。 我將把它留在這里,以防其他人犯類似的錯誤。
由於我已經設置了每次創建時都刪除數據庫中所有內容的代碼,因此:
database.execSQL("DELETE FROM " + Table_mm_recipes.TABLE_NAME);
database.execSQL("DELETE FROM " + Table_mm_ingredient_in_recipe.TABLE_NAME);
database.execSQL("DELETE FROM " + Table_mm_ingredients.TABLE_NAME);
數據出了點問題。 這樣做實際上沒有任何意義,因為您可以只創建數據庫並在SQLiteOpenHelper.onCreate()
插入數據就可以了。 如果需要在設置任何版本控制之前更新數據,只需卸載並重新安裝該應用程序即可。 然后,可以根據需要在SQLiteOpenHelper.onUpgrade()
銷毀數據。 我不確定數據是如何被弄亂的,但是確實可以。
什么是奇怪,雖然,是,我仍然可以看到通過做一個簡單的數據庫已經在其數據
Cursor cursor = database.rawQuery("SELECT recipe_id, ingredient_id, name FROM mm_ingredient_in_recipe_groups", null);
並從之前迭代該光標。 我在INNER JOIN
語句之前直接對所有表執行了此操作,但是它們仍然無法正常工作。 這可能與錯誤刪除/創建數據庫有關。
除此之外,以上所有代碼均應有效並且可以工作。
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