Question

我正在尝试解决SQL问题，但是遇到这个问题时，我遇到了麻烦。

问题是：给一个表Plays包含3列id，title和writer。第二个表是reservation，其中有4列：

id, play_id (same is as in play table), number_of_tickets, theater

现在的问题是要找到包含ID（从播放表），title（从播放表）和reserved_tickets（必须按降序）的列组成的表。

Answer 1

我将对play的查询和对reservation的聚合查询进行联接：

SELECT   id, title, reserved_tickets
FROM     play p
JOIN     (SELECT   play_id, SUM(number_of_tickets) AS reserved_tickets
          FROM     reservations
          GROUP BY play_id) r ON p.id = r.play_id
ORDER BY 2 DESC

Answer 2

这通常用JOIN和GROUP BY来表达：

SELECT p.id, p.title, COUNT(*) as reserved_tickets
FROM play p JOIN
     reservations r
     ON p.id = r.play_id
GROUP BY p.id, p.title
ORDER BY COUNT(*) DESC

如何将带计数的SQL表加入？

2 个答案: