Question

这是一个涉及连接的SQL问题，比我想要的更多。

我有2个表，一个事件表和歌手表

EVENTS
event_id
event_name
num_attendees
tickets_sold
tickets_promo
event_date
... many other fields

SINGERS
event_id
singer

我正在尝试从事件表中获取事件统计信息，如果执行了任何歌手列表。

EVENTS:
event_id num_attendees tickets_sold
   1        15              2500
   2         5              1575

Singers at the event:
event_id  singer
   1      bob
   1      jane
   2      bob

我对bob或jane演唱的事件的统计感兴趣：

SELECT count(e.event_id) as count_events, sum(num_attendees) as sum_attentees, 
       sum(tickets_sold) as sum_tickets_sold
  FROM `events` e
       INNER JOIN singers s ON s.event_id = e.event_id 
   AND s.singer IN ("bob", "jane")
 WHERE event_date ...

给我一个错误的计数和总和，因为加入会给我2个事件1的记录，1个事件2的记录和事件的数量将是3。

我该如何编写这个SQL？感谢。

Answer 1

SELECT count(e.event_id) as count_events,
       sum(num_attendees) as sum_attentees,
       sum(tickets_sold) as sum_tickets_sold 
FROM events e 
WHERE e.event_id IN 
     (SELECT DISTINCT event_id FROM singers WHERE singer IN ("bob", "jane"));

Answer 2

SELECT count(e.event_id) as count_events, 
       sum(num_attendees) as sum_attentees, 
       sum(tickets_sold) as sum_tickets_sold
  FROM `events` e
 WHERE event_date ...
   AND EXISTS (
           SELECT 1 
             FROM singers s 
            WHERE s.event_id = e.event_id 
              AND s.singer IN ("bob", "jane")
              );

Answer 3

我不认为JOIN真的适合这里。尝试使用子查询来获取您感兴趣的事件列表：

SELECT count(e.event_id) as count_events, sum(num_attendees) as sum_attentees,
    sum(tickets_sold) as sum_tickets_sold
    FROM events WHERE event_id IN
        (SELECT DISTINCT event_id FROM singers WHERE singer_id IN ('Bob', 'Jane'))
    AND event_date ...

Answer 4

我认为您也可以使用加入如

 SELECT count(e.event_id) as count_events, 
   sum(e.num_attendees) as sum_attentees, 
   sum(e.tickets_sold) as sum_tickets_sold
 FROM events e join (SELECT DISTINCT event_id FROM singers WHERE singer_id IN ('Bob', 'Jane')) s 
  on e.event_id =  s.event_id

mysql - 我不希望连接上有多条记录

4 个答案: