MySQL中的自聯接計數

Question

我正在嘗試做類似的事情

SELECT `v1`.`date`, COUNT(DISTINCT(`v2`.`id`)) AS `visits` 
FROM `visitor_visits` AS `v1` JOIN `visitor_visits` AS `v2` 
ON (`v1`.`date` = `v2`.`date`) GROUP BY `v1`.`date`, `v2`.`date` 
ORDER BY `v1`.`date

獲取不同的日期，以及匹配的所有其他日期的計數。

我很確定這是錯誤的查詢，因為日期列是非唯一的。

Answer 1

有什么不對：

SELECT v1.date, COUNT(v1.id) AS visits 
FROM visitor_visits AS v1
GROUP BY v1.date
ORDER BY v1.date

？

PS。 我假設id是主鍵（唯一）。

Answer 2

如果您查看每個日期的不同訪客ID，則應該是

SELECT v1.date,
       COUNT(DISTINCT(v1.id)) as Visitors
   FROM
      visitor_visits AS v1
   group by
      v1.Date