Question

我有这个查询来计算一周和几小时中最常见的日子：

SELECT
  DATE_FORMAT(DATE, '%a') AS wd,
  HOUR(DATE) AS hr,
  COUNT(*) AS cnt
FROM 
 users
GROUP BY
  wd, hr
ORDER BY
  cnt DESC

现在，我想选择与wd = "Fri" AND hr = "9"

匹配的所有行的ID

我已经尝试添加WHERE子句，但我不能，因为我不能在别名上使用WHERE。

Answer 1

SELECT ID
FROM   users
WHERE  DATE_FORMAT(DATE, '%a') = 'Fri' AND HOUR(DATE) = 9

Answer 2

SELECT
  DATE_FORMAT(DATE, '%a') AS wd,
  HOUR(DATE) AS hr,
  COUNT(*) AS cnt
FROM users
WHERE DATE_FORMAT(DATE, '%a') = 'Fri'
AND HOUR(DATE) = 9
GROUP BY wd, hr
ORDER BY cnt DESC

您也可以使用别名选择来执行此操作，但性能不一样好，因为这种方式在聚合之前发生

选择与计算匹配的行

2 个答案: