我正在尝试在MySQL数据库中选择约会之间的前十个空时隙。
约会表基本上有3个字段:appointment_id INT,startDateTime DATETIME和endDateTime DATETIME。
我们可以想象一些像这样的数据(为了简单起见,我将日期部分留在日期时间之外,所以让我们考虑这些时间是在同一天)。此外,数据按startDateTime排序:
4 | 09:15:00 | 09:30:00
5 | 09:30:00 | 09:45:00
8 | 10:00:00 | 10:15:00
3 | 10:30:00 | 10:45:00
7 | 10:45:00 | 11:00:00
2 | 11:00:00 | 11:15:00
1 | 11:30:00 | 12:00:00
所以我的目标是提取:
00:00:00 | 09:15:00
09:45:00 | 10:00:00
10:15:00 | 10:30:00
11:15:00 | 11:30:00
最终做到了这一点:
SET @myStart = '2012-10-01 09:15:00';
SET @myEnd = NULL;
SET @prevEnd = NULL;
SELECT a.endDateTime, b.startDateTime, @myStart := a.endDateTime
FROM appointment a, appointment b, (
SELECT @myEnd := min(c.startDateTime)
FROM appointment c
WHERE c.startDateTime >= @myStart
ORDER BY startDateTime ASC
) as var ,
(SELECT @prevEnd := NULL) v
WHERE a.appointment_id = (
SELECT appointment_id
FROM (
SELECT appointment_id, max(endDateTime), @prevEnd := endDateTime
FROM appointment d
WHERE (@prevEnd IS NULL OR @prevEnd = d.startDateTime)
AND d.startDateTime >= @myEnd
) as z
)
AND b.startDateTime > a.endDateTime
ORDER BY b.startDateTime ASC LIMIT 0,10;
这不会返回任何结果。我想这是因为我的用户定义变量的初始化不正确(刚发现它们,我可能完全错误地使用它们)。
如果我只运行第一个子查询,其目的是在@myStart之后的第一次约会时初始化@myEnd,我可以看到它实际上在09:15:00返回。
第二个子查询(SELECT @prevEnd := NULL) v
用于在每次在主查询中选择行时将@prevEnd设置为NULL。我不太确定它是那样的......
最后一个子查询的意思是,从null @prevEnd和一个初始化的@myEnd开始,选择之后存在间隙的约会。如果与查询的其余部分分开,我可以验证它是否也能正常工作。
您对我可以采取哪些措施来解决问题的建议有什么建议,关于我怎样才能/应该这样做,或者甚至是否可能这样做?
非常感谢。
修改:我已按照以下方式对其进行了编辑:
SELECT *
FROM (
SELECT COALESCE( s1.endDateTime, '0000-00-00 00:00:00' ) AS myStart, MIN( s2.startDateTime ) AS minSucc
FROM appointment s1
RIGHT JOIN appointment s2 ON s1.endDateTime < s2.startDateTime
AND s1.radiologyroom_id = s2.radiologyroom_id
WHERE s1.startDateTime >= '2012-10-01 00:00:00'
AND s1.radiologyroom_id =174
AND s1.endDateTime < '2013-01-01 00:00:00'
GROUP BY myStart
ORDER BY s1.startDateTime
)s
WHERE NOT
EXISTS (
SELECT NULL
FROM appointment
WHERE startDateTime >= myStart
AND endDateTime <= minSucc
AND radiologyroom_id =174
ORDER BY startDateTime
)
它在14.6秒内从6530条记录中检索369行
答案 0 :(得分:1)
如果ids
之间没有差距,且id
总是在增加,您可以使用此功能:
SELECT coalesce(s1.endDateTime, '0000-00-00 00:00:00'), s2.startDateTime
FROM
slots s1 right join slots s2
on s1.appointment_id=s2.appointment_id-1
WHERE coalesce(s1.endDateTime, '0000-00-00 00:00:00')<s2.startDateTime
LIMIT 10
编辑:您也可以尝试:
SELECT * FROM
(SELECT
coalesce(s1.endDateTime, '0000-00-00 00:00:00') as start,
min(s2.startDateTime) minSucc
from slots s1 right join slots s2
on s1.endDateTime<s2.startDateTime
group by start) s
WHERE
not exists (select null
from slots
where startDateTime>=start
and endDateTime<=minSucc)
EDIT2:我承认我对变量的查询并不多,但看起来它可以起作用:
select d1, d2 from (
select
@previous_end as d1,
s.startDateTime as d2,
@previous_end:=s.endDateTime
from (select startDateTime, endDateTime from slots order by startDateTime) s,
(select @previous_end := '0000-00-00 00:00:00') t) s
where d1<d2