Question

我正在尝试创建一个Produces：

的查询

VENUE | 2012-10-01 | 2012-10-02 | 2012-10-03
 01   |  OCCUPIED  |   EMPTY    |  OCCUPIED
 02   |   EMPTY    |   EMPTY    |  OCCUPIED
 03   |  OCCUPIED  |   EMPTY    |   EMPTY

来自这两个表：

地点表：

venue_id | venue
   1     |   01
   2     |   02
   3     |   03

活动表：

event_id |    start   |    end     | venue_id
   1     | 2012-10-01 | 2012-10-02 |    1
   2     | 2012-10-03 | 2012-10-04 |    1
   3     | 2012-10-03 | 2012-10-04 |    2
   4     | 2012-10-01 | 2012-10-02 |    3

有人能提出解决这个问题的最佳方法吗？

我目前的做法是：

SELECT 
   venue,
   IF(start <= '2012-10-01' AND '2012-10-01' < end, 'OCCUPIED','EMPTY') AS '2012-10-01',
   IF(start <= '2012-10-02' AND '2012-10-02' < end, 'OCCUPIED','EMPTY') AS '2012-10-02',
   IF(start <= '2012-10-03' AND '2012-10-03' < end, 'OCCUPIED','EMPTY') AS '2012-10-03'
FROM Venue as v, Event as e
WHERE e.venue_id = v.venue_id
GROUP BY v.venue

然而，我没有得到理想的结果......我得到了以下内容：

VENUE | 2012-10-01 | 2012-10-02 | 2012-10-03
 01   |  OCCUPIED  |   EMPTY    |   EMPTY
 02   |   EMPTY    |   EMPTY    |  OCCUPIED
 03   |  OCCUPIED  |   EMPTY    |   EMPTY

我做错了什么？

Answer 1

奇怪的是，你的select语句甚至没有返回你发布的结果集中命名的列。此外，我注意到您正在重复查询“2012-10-02”。

SELECT 
   IF(start <= '2012-10-01' AND '2012-10-01' < end, 'OCCUPIED','EMPTY') AS '2012-10-01',
   IF(start <= '2012-10-02' AND '2012-10-02' < end, 'OCCUPIED','EMPTY') AS '2012-10-02',
   IF(start <= '2012-10-03' AND '2012-10-03' < end, 'OCCUPIED','EMPTY') AS '2012-10-03'
FROM Venue as v, Event as e
WHERE e.venue_id = v.venue_id
GROUP BY v.venue

修改

以下两个活动共享相同的venue_id和场地，您的查询按场地分组，这样就可以在2012-10-03'日压制OCCUPIED结果。

event_id | start | end | venue_id 1 | 2012-10-01 | 2012-10-02 | 1 2 | 2012-10-03 | 2012-10-04 | 1

SQL FIDDLE：http://sqlfiddle.com/#!2/dc33f/20

你可以尝试添加像MAX这样的聚合函数来获取记录子集中包含的任何OCCUPIED事件：

SELECT e.*, v.venue, max(IF(start <= '2012-10-01' AND '2012-10-01' < end, 'OCCUPIED','EMPTY')) AS '2012-10-01', max(IF(start <= '2012-10-02' AND '2012-10-02' < end, 'OCCUPIED','EMPTY')) AS '2012-10-02', max(IF(start <= '2012-10-03' AND '2012-10-03' < end, 'OCCUPIED','EMPTY')) AS '2012-10-03' from event e, venue v where e.venue_id = v.venue_id GROUP BY v.venue

SQL FIDDLE：http://sqlfiddle.com/#!2/dc33f/22

创建一个处理包含多个事件的日历的MySQL查询

1 个答案: