我有一个表,每一行存储了一个带有开始日期/时间和结束日期/时间的会议。
meetingID int
meetingStart datetime
meetingEnd datetime
期望输出:
对于每一对重叠的行,我想输出
meetingID,meetingStart,meetingID,meetingEnd
在MySQL中执行这样的查询最有效的方法是什么?
我有一个表,每一行存储了一个带有开始日期/时间和结束日期/时间的会议。
meetingID int
meetingStart datetime
meetingEnd datetime
期望输出:
对于每一对重叠的行,我想输出
meetingID,meetingStart,meetingID,meetingEnd
在MySQL中执行这样的查询最有效的方法是什么?
SELECT m1.meetingID, m1.meetingStart, m1.meetingEnd, m2.meetingID
FROM t_meeting m1, t_meeting m2
WHERE (m2.meetingStart BETWEEN m1.meetingStart AND m1.meetingEnd
OR m2.meetingEnd BETWEEN m1.meetingStart AND m1.meetingEnd)
AND m1.meetingID <> m2.meetingID
这会重复选择每对元素。
如果你想只选择每对元素一次,请使用:
SELECT m1.meetingID, m1.meetingStart, m1.meetingEnd, m2.meetingID
FROM t_meeting m1, t_meeting m2
WHERE (m2.meetingStart BETWEEN m1.meetingStart AND m1.meetingEnd
OR m2.meetingEnd BETWEEN m1.meetingStart AND m1.meetingEnd)
AND m2.meetingID > m1.meetingID
确保在查询中对 meetingStart
和 meetingEnd
创建了索引,以使查询运行更加高效。
然而,MySQL
可能会使用 INDEX MERGE
来运行此查询,但是在目前的实现方式下这不是非常高效的。
你也可以尝试使用:
SELECT m1.*, m2.*
FROM (
SELECT m1.meetingID AS mid1, m2.meetingID AS mid2
FROM t_meeting m1, t_meeting m2
WHERE m2.meetingStart BETWEEN m1.meetingStart AND m1.meetingEnd
AND m2.meetingID <> m1.meetingID
UNION
SELECT m1.meetingID, m2.meetingID
FROM t_meeting m1, t_meeting m2
WHERE m2.meetingEnd BETWEEN m1.meetingStart AND m1.meetingEnd
AND m2.meetingID <> m1.meetingID
) mo, t_meeting m1, t_meeting m2
WHERE m1.meetingID = mid1
AND m2.meetingID = mid2
还有一种更为复杂的方法,但很可能会运行得更快。
尝试使用此查询。这是Quassnoi的解决方案,已修改为忽略一个预订的结束与另一个预订的开始相同的情况。
SELECT m1.meetingID_id, m1.meetingStart , m1.meetingEnd, m2.meetingID_id
FROM bookings m1, bookings m2
WHERE (m2.meetingStart BETWEEN m1.start AND DATE_SUB(m1.meetingEnd, INTERVAL 1 second)
OR DATE_SUB(m2.meetingEnd, INTERVAL 1 second) BETWEEN m1.meetingStart AND m1.end)
AND m1.meetingID_id > m2.meetingID_id
可能是这样的:
SELECT m1.meetingID, m2.meetingID
FROM meeting AS m1, meeting AS m2
WHERE m1.meetingID < m2.meetingID
AND m1.meetingStart BETWEEN m2.meetingStart AND m2.meetingEnd
OR m1.meetingEnd BETWEEN m2.meetingStart AND m2.meetingEnd
m1.meetingID < m2.meetingID
,您不会将行与其自身进行比较,并且不会获得重复项,因为每行都会被连接两次(m1,m2)和(m2,m1)。SELECT m1.meetingID AS firstID, m1.meetingStart AS firstStart,
m1.meetingEnd AS firstEnd, m2.meetingID AS secondID,
m2.meetingStart AS secondStart, m2.meetingEnd AS secondEnd
FROM meeting AS m1, meeting AS m2
WHERE (m2.meetingStart BETWEEN m1.meetingStart AND m1.meetingEnd)
AND (m1.meetingID != m2.meetingID)
这样,m2将始终是在m1之后或同时开始的, 而m1.id!= m2.id确保它不会包含与自身匹配的内容。
您无需检查会议结束时间,因为可以通过仅比较会议开始时间可靠地检测到重叠。