mysql - 限制sql中统计的记录数

Question

在我的数据库中，我可以很容易地看到我的表中的最后 50 个人，state=NY 和 postcode=12405，我可以查看表以查看他们是否有狗。

    SELECT state, postcode, havedog
    FROM address
    WHERE (state=NY) AND (postcode=12405)
    ORDER BY surname DESC
    LIMIT 0 , 5

哪个返回

state   postcode    havedog
NY  12405   yes
NY  12405   yes
NY  12405   no
NY  12405   no
NY  12405   yes

我还可以计算我的整个数据库中有多少人有一只狗，其中 state=NY 和 postcode=12405

    SELECT state, postcode COUNT(havedog) AS DOG
    FROM address
    WHERE (state=NY AND postcode=12405 ) AND (havedog=yes)

但是我不知道如何限制计数，所以它只计算 state=NY 和 postcode=12405 和 havedog=yes 的最后 5 条记录，是否可以对 Count 函数应用限制？

例如，鉴于上表，我的计数结果应该是 3。

Answer 1

使用子选择：

SELECT COUNT(*) FROM
(
    SELECT state, postcode, havedog
    FROM address
    WHERE state = 'NY' AND postcode = 12405
    ORDER BY surname DESC
    LIMIT 5
) T1
WHERE havedog = 1

Answer 2

你可以这样做：

SELECT
  state,
  postcode
  COUNT(havedog) AS DogCounts
FROM
(
  SELECT state, postcode, havedog
  FROM address
  WHERE (state=NY) AND (postcode=12405)
  ORDER BY surname DESC
  LIMIT 50
) t
GROUP BY state, postcode

Answer 3

SELECT top 50 state, postcode, COUNT(havedog) OVER () AS DOG
FROM address 
WHERE (state='NY' AND postcode=12405 ) AND (havedog='yes')