SQL Nested Query with invalid relation error (ORA-00920 Error)

Question

I have 3 tables in total. I am trying to select the price of the cost food has to be the highest and the category name have to fall under organic.

I have came up with the following SQL QUERY but i have received an invalid relation error.

Could someone point me out what the problem might be ?

Thanks

SELECT PRICE, LABEL
FROM FOOD
WHERE FOOD.FOOD_ID = (
    SELECT FOOD_ID
    FROM FOOD_CATEGORY
    WHERE FOOD_CATEGORY.FOOD_ID = (
       SELECT FOOD_ID
       FROM CATEGORY
       WHERE NAME = 'ORGANIC'
    )
);

FOOD

• FOOD_ID
• LABEL
• PRICE

FOOD_CATEGORY

• FOOD_ID
• CATEGORY_ID

CATEGORY

• CATEGORY_ID
• NAME

Relationship

FOOD.FOOD_ID = FOOD_CATEGORY.FOODID 

FOOD_CATEGORY.CATEGORYID = CATEGORY.CATEGORYID

Answer 1

I suspect you have more foods that are of category 'ORGANIC'. Otherwise there is no need for the table FOOD_CATEGORY. The table FOOD_CATEGORY is there to create a many-to-many relation.

So why not :

SELECT PRICE, LABEL
FROM FOOD
JOIN FOOD_CATEGORY ON (FOOD_CATEGORY.FOOD_ID = FOOD.FOOD_ID)
JOIN CATEGORY ON (CATEGORY.CATEGORY_ID = FOOD_CATEGORY.CATEGORY_ID)
WHERE CATEGORY.NAME = 'ORGANIC';

Or use IN instead of =

SELECT PRICE, LABEL
FROM FOOD
WHERE FOOD.FOOD_ID IN (
    SELECT FOOD_ID
    FROM FOOD_CATEGORY
    WHERE FOOD_CATEGORY.CATEGORY_ID = (
       SELECT CATEGORY_ID
       FROM CATEGORY
       WHERE NAME = 'ORGANIC'
    )
);

Answer 2

because its CATEGORY_ID instead of FOOD_ID

SELECT PRICE, LABEL
FROM FOOD
WHERE FOOD.FOOD_ID = (
    SELECT FOOD_ID
    FROM FOOD_CATEGORY
    WHERE FOOD_CATEGORY.FOOD_ID = (
       SELECT CATEGORY_ID
       FROM CATEGORY
       WHERE NAME = 'ORGANIC'
    )
);