Select records only if all matching records are same value

Question

I have the following table:

id	food	type	nutrition
1	chicken	meat	healthy
2	salad	vegetable	healthy
3	burger	meat	unhealthy

I want to query all types of food which are completely healthy. The expected result here is only vegetable because burger is considered unhealthy even if chicken is healthy.

Answer 1

In MySQL or Postgres, we can try aggregating:

SELECT type
FROM yourTable
GROUP BY type
HAVING SUM(nutrition <> 'healthy') = 0;