mysql - 如何找到只有男性顾客的商店？

Question

我有这个架构:

人员(姓名、性别)

频率(名称、商店)

我的问题是，如何找到顾客全部为男性的商店？

Answer 1

您可以将 GROUP BY 与 HAVING 结合使用:

SELECT frequents.shop
FROM frequents LEFT JOIN person ON frequents.name = person.name 
GROUP BY frequents.shop
HAVING SUM(person.sex = 'female') = 0 AND SUM(person.sex = 'male') > 0

demo at dbfiddle.uk