查找仅包含纯素产品的所有食谱

Question

I have been trying to find all recipes with just vegan products but so far I just have this:

SELECT DISTINCT r.*
FROM recipes r INNER JOIN recipe_product rp ON r.id = rp.recipe_id
INNER JOIN products p ON rp.product_id = p.id 
INNER JOIN product_specificdiet ps ON p.id = ps.product_id 
INNER JOIN specificdiets sd ON ps.specific_diet_id = sd.id 
WHERE sd.type = 'VEGAN';

But that query is giving me all the products that are vegan for all the recipes.

No idea how could I resolve it.

Thanks!

Answer 1

Two rules:

1. A product is vegan, if one of its specific diets is 'VEGAN'.
2. A recipe is vegan, if it only consists of vegan products.

In other words: A vegan recipe is a recipe for which NOT EXISTS any product that is NOT IN the set of vegan products.

select *
from recipes r
where not exists
(
  select null -- non-vegan ingredient
  from recipe_product rp 
  where rp.recipe_id = r.id
  and rp.product_id not in 
  (
    select ps.product_id -- vegan product
    from product_specificdiet ps
    join specificdiets sd ON ps.specific_diet_id = sd.id 
    where sd.type = 'VEGAN'
  )
);

Answer 2

SELECT
    re.*
FROM
    recipes re
WHERE
    re.id NOT IN (
        SELECT
            r.id
        FROM
            recipes r
        LEFT JOIN
            recipe_product rp ON r.id = rp.recipe_id
        LEFT JOIN
            products p ON rp.product_id = p.id 
        LEFT JOIN
            product_specificdiet ps ON p.id = ps.product_id 
        LEFT JOIN
            specificdiets sd ON ps.specific_diet_id = sd.id 
        WHERE 
            ISNULL(sd.type, '') != 'VEGAN';
    )

Answer 3

Use aggregation and a HAVING clause:

SELECT r.*
FROM recipes r JOIN
     recipe_product rp
     ON r.id = rp.recipe_id JOIN
     products p
     ON rp.product_id = p.id JOIN
     product_specificdiet ps
     ON p.id = ps.product_id JOIN
     specificdiets sd
     ON ps.specific_diet_id = sd.id 
GROUP BY r.id
HAVING COUNT(*) FILTER (sd.type = 'VEGAN') = COUNT(*);

An alternative method would filter out ingredients that are not vegan and check for zero of them:

HAVING COUNT(*) FILTER (sd.type <> 'VEGAN') = 0;

Postgres is one of the databases that allows you to specify SELECT r.* even though you are only aggregating by r.id -- because that is allowed when the aggregation key is a primary key. In other databases, you may need to list the columns both in the SELECT and the GROUP BY if you want additional columns.

Answer 4

Maybe by joining to a sub-query. One that uses a filters the specific diets that only uses vegan types.

Untested notepad scribble :

SELECT r.*
FROM recipes r 
JOIN
(
  SELECT rp.recipe_id
  FROM recipe_product rp
  INNER JOIN products p 
    ON p.id = rp.product_id
  INNER JOIN product_specificdiet ps 
    ON ps.product_id = p.id
  LEFT JOIN specificdiets sd 
    ON sd.id = ps.specific_diet_id
  GROUP BY rp.recipe_id
  HAVING COUNT(CASE WHEN sd.type = 'VEGAN' THEN sd.id END) = COUNT(*)
) q
ON q.recipe_id = r.id;