Question

I have a diners table:

NAME     |   FOOD
-----------------
matthew  |   rice
matthew  |   beans
mark     |   rice
mark     |   beans
Luke     |   rice
john     |   beans

I need to extract names that have had only rice, names that have had only beans and both. A LEFT JOIN would work if they were in separate tables. But I’m having difficulty because they’re in one table.

I’ve tried variants of these 2 statements with no luck:

SELECT name 
FROM diners 
WHERE NOT EXISTS 
    (SELECT name 
     FROM diners
     WHERE food = 'beans')

SELECT t1.name FROM diners AS t1
LEFT JOIN diners AS t2 ON t1.name = t2.name
WHERE t2.food = 'rice'
  AND t2.name IS NULL

Answer 1

— names that have had BOTH

SELECT NAME FROM diners
WHERE FOOD IN ('RICE','BEANS')
GROUP BY NAME
HAVING COUNT(*)>1

— names that have had only rice

SELECT NAME FROM diners
WHERE NAME NOT IN (
SELECT NAME FROM diners
WHERE FOOD NOT IN ('RICE'))

–names that have had only beans

SELECT NAME FROM diners
WHERE NAME NOT IN (
SELECT NAME FROM diners
WHERE FOOD NOT IN ('BEANS'))