mysql - 基于一个元素的查询

Question

我得到了以下数据库架构

Cows (cowID, cowName, cowAge)
CowPurchaser (purchaserID, name, address)
PurchaseRecord (purchaserID, cowID, year)

每年，奶牛购买者“FARMLAND”至少购买一头奶牛，求出购买的奶牛数量。输出为元组集合，表示“FARMLAND”购买的牛的年份和数量

我不知道如何解决这个问题。我试过了

SELECT (pr.year, COUNT(c.name))
FROM PurchaseRecord pr, CowPurchaser cp, Cows c
WHERE cp.name = "FARMLAND" AND COUNT(c.name) >= 1

这没有给出我想要的结果。我可能做错了什么？我该如何修复它？

Answer 1

SELECT pr.year, COUNT(c.name)
FROM PurchaseRecord pr
     INNER JOIN CowPurchaser cp ON pr.purchaserID=cp.purchaserID
     INNER JOIN Cows c ON pr.cowID=c.cowID
WHERE cp.name = "FARMLAND" 
GROUP BY pr.year
HAVING COUNT(c.name) >= 1