MySQL САМО IN() еквивалентна клауза

този проблем се нарича Relational Division

SELECT boy_id 
FROM   boys_chocolates 
WHERE  chocolate_id IN ('$string')
GROUP  BY boy_id 
HAVING COUNT(DISTINCT chocolate_id) = ? -- <<== number of chocolates specified

пример:

SELECT boy_id 
FROM   boys_chocolates 
WHERE  chocolate_id IN (1,2,3,4)
GROUP  BY boy_id 
HAVING COUNT(DISTINCT chocolate_id) = 4

• SQL на релационно подразделение

обаче, ако chocolate_id е уникален за всеки boy_id , DISTINCT ключовата дума не е задължителна.

SELECT boy_id 
FROM   boys_chocolates 
WHERE  chocolate_id IN (1,2,3,4)
GROUP  BY boy_id 
HAVING COUNT(*) = 4

АКТУАЛИЗИРАНЕ 1

...Искам да избера момчета от масата, които иматточно шоколадите, които споменавам. Не повече, не по-малко...

SELECT boy_id 
FROM   boys_chocolates a
WHERE  chocolate_id IN (1,2,3,4) AND
        EXISTS 
        (
            SELECT  1
            FROM    boys_chocolates b
            WHERE   a.boy_ID = b.boy_ID
            GROUP   BY boy_id
            HAVING  COUNT(DISTINCT chocolate_id) = 4
        )
GROUP  BY boy_id
HAVING COUNT(*) = 4

• SQLPiddle Демо