Question

在我的数据库中，我可以很容易地看到我桌上的最后50个人状态= NY和邮编= 12405，我可以向下看桌子，看看他们是否有狗。

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

返回

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

我还可以统计我的整个数据库中有多少人有一只狗，其中州=纽约，邮政编码= 12405

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

但是我无法弄清楚如何限制计数，因此它只计算最近5条记录，其中state = NY，postcode = 12405和havedog = yes，是否可以对Count函数应用限制？

例如，如上表所示，我的计数结果应为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')

限制在sql中计算的记录数

3 个答案: