在Android中使用SQLite中的INNER JOIN时遇到问题

Question

我在本地服务器上有一个MySQL数据库。我使用PHP和JSON over HTTP从MySQL数据库获取数据。在Android应用中，使用JSON结果填充SQLite数据库。我已经验证SQLite数据库实际上是通过运行类似于

Cursor cursor = database.rawQuery("SELECT recipe_id, ingredient_id, name FROM mm_ingredient_in_recipe_groups", null); 

的测试查询填充的，然后迭代结果光标以查看数据是否存在。存在的数据存储在三个表中：

1. mm_ingredients，包含食谱成分。
2. mm_recipes，包含食谱数据。
3. mm_ingredient_in_recipe，其中包含用于连接mm_recipes和mm_ingredients（即解决多对多关系）中的数据的数据。

我想要做的是运行一个查询，选择参数配方名称的成分。这意味着我必须INNER JOIN mm_ingredients与mm_ingredient_in_recipe和mm_recipes。

我试图运行下面的查询：

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"}); 

这将返回一个空指针。然而，在我的MySQL数据库中，运行相应的查询

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"; 

返回预期数据。我在这里做错了什么？看起来像我运行的每个查询都正常工作，直到我开始包括INNER JOIN。 （ID字段被命名为SQLite中_id，如应该是最好的做法，据我所知）。

编辑：添加代码写入到数据库：

下面是我如何填充一个例子数据库为表mm_recipes。其他两个表格也是如此。我使用JSONArray.optString()为SQLite的TEXT数据类型，JSONArray.optInt()为INTEGER和JSONArray.optDouble()为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); 
    } 

} 

作为参考，这里也是如何创建mm_recipe表的示例。在我的类mm_recipe：

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SQLiteOpenHelper类：

@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); 
} 

Answer 1

这竟然是（预期）一些愚蠢的错误。如果其他人发生类似的错误，我会在这里留下。

既然我已经设置代码上创作每次数据库删除所有内容，以这种方式：

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); 

坏事发生在数据不知何故。这样做并没有什么意义，因为您可以创建数据库并在SQLiteOpenHelper.onCreate()处插入数据，并且没问题。如果您需要在设置任何版本之前更新数据，请卸载并重新安装应用程序。如果您愿意，您可以在SQLiteOpenHelper.onUpgrade()销毁数据。我不知道如何数据搞砸了，但他们当然是。

什么是奇怪不过，是我仍然可以看到数据库做一个简单的

Cursor cursor = database.rawQuery("SELECT recipe_id, ingredient_id, name FROM mm_ingredient_in_recipe_groups", null); 

和迭代，从之前光标曾在它的数据。我在INNER JOIN声明之前直接对所有表格进行了这项操作，但它们仍然无效。它可能与错误地删除/创建数据库有关。

除此之外，上面的所有代码都应该是有效的并且可以工作。