使用多个表获取数据SQLitedatabase

Question

I have three tables in my database: Category, Words, and WordImgs. I'm trying to implement ListgetAllCategories and the problem is I need to retrieve data from all three tables in order to do this. Am I suppose to join the 3 tables? Not quite sure how to accomplish this.

Each Category contains a name and an arraylist of words. Each word contains a name an arraylist of images.

Statements used to create tables:

public void onCreate(SQLiteDatabase db) {
    final String SQL_CREATE_CATEGORY_TABLE = "CREATE TABLE " + CATEGORIES_TABLE + " (" +
            _ID + " INTEGER PRIMARY KEY AUTOINCREMENT," +
            TITLE + " TEXT NOT NULL " + ");";
    final String SQL_CREATE_WORDS_TABLE = "CREATE TABLE " + WORDS_TABLE + " (" +
            _ID + " INTEGER PRIMARY KEY AUTOINCREMENT," +
            TITLE + " TEXT NOT NULL, " +
            BELONGS_TO + " INTEGER NOT NULL, " +
            "FOREIGN KEY (" + BELONGS_TO + ") REFERENCES " + CATEGORIES_TABLE + " (" + _ID + ")" +
            ");";
    final String SQL_CREATE_WORDIMG_TABLE = "CREATE TABLE " + WORDIMGS_TABLE + " (" + _ID + " " +
            "INTEGER PRIMARY KEY AUTOINCREMENT," + TITLE + " TEXT NOT NULL, " +
            BELONGS_TO + " INTEGER NOT NULL, " +
            "FOREIGN KEY (" + BELONGS_TO + ") REFERENCES " + WORDS_TABLE + " (" + _ID + ")" +
            ");";



    db.execSQL(SQL_CREATE_CATEGORY_TABLE);
    db.execSQL(SQL_CREATE_WORDS_TABLE);
    db.execSQL(SQL_CREATE_WORDIMG_TABLE);

}

Answer 1

you can join the 3 tables like this:

select *
from CATEGORIES_TABLE c
join WORDS_TABLE w on c.ID = w.BELONGS_TO
join WORDIMGS_TABLE wi on w.ID = wi.BELONGS_TO

Answer 2

You should really read up on joins :-)

You're actually mixing variables in with the SQL there, so I don't actually know what your column names and whatnot are, but I'll give you a quick-and-dirty example that should give you an idea.

Let's say you want all the image titles for words in the category "foo":

select wordimgs_table.title
from categories_table
inner join words_table on words_table.belongs_to = categories_table._id
inner join wordimgs_table on wordimgs_table.belongs_to = categories_table._id
where categories_table.title = 'foo'

This will give you basically an unordered list. Add in your own order by clause and friends. And obviously substitute the actual table and column names, etc etc.