问题描述
我认为以下是您想要的:
SELECT *, (To_days(date_expires)-TO_DAYS(Now())) as dayDiff, COUNT(id) AS change_count
FROM mytable
GROUP BY (case when source_id is null then id else source_id end)
HAVING dayDiff < 4
ORDER BY (case when source_id is null then 1 else 0 end), date_created DESC
它是有条件的,group by
因此NULL sourceids将不会被分组。然后,使用中的逻辑将它们置于最后order by
。
我不明白您最后一次发生的意思。现在我想我做了:
SELECT coalesce(s.id, mytable.id) as id,
max(case when s.maxid is not null and s.maxid = myable.id then mytable.name
when s.maxid is null then NULL
else mytable.name
end) as name,
(To_days(date_expires)-TO_DAYS(Now())) as dayDiff, COUNT(id) AS change_count
FROM mytable left outer join
(select source_id, MAX(id) as maxid
from mytable
where source_id is not null
group by source_id
) s
on mytable.id = s.maxid
GROUP BY (case when source_id is null then id else source_id end)
HAVING dayDiff < 4
ORDER BY (case when source_id is null then 1 else 0 end), date_created DESC
这将加入最新记录中的信息(基于最高ID)。
解决方法
我有一个数据库:
+--+----+---------+
|id|name|source_id|
+--+----+---------+
|11|aaaa|null
+--+----+---------+
|12|bbbb|1
+--+----+---------+
|13|cccc|1
+--+----+---------+
|14|dddd|null
+--+----+---------+
|15|eeee|2
+--+----+---------+
|16|ffff|2
+--+----+---------+
|17|gggg|2
+--+----+---------+
我想选择所有条目,但有一个例外:
- 与的所有条目
source_id == somevalue(not null)
均应分组 - *与的 *最后一个条目
source_id == null
应在之后
这是我期望的结果:
+----+--+----+---------+
COUNT|id|name|source_id|
+----+--+----+---------+
.....|11|aaaa|null
+----+--+----+---------+
.2...|13|cccc|1
+----+--+----+---------+
.....|14|dddd|null
+----+--+----+---------+
.3...|17|ffff|2
+----+--+----+---------+
到目前为止,我已经做到了这一点(注意:“ change_count” = COUNT):
SELECT *,(To_days(date_expires)-TO_DAYS(NOW())) as dayDiff,COUNT(id) AS change_count FROM mytable
GROUP BY source_id
HAVING dayDiff < 4
ORDER BY date_created DESC
那就是我得到的:
+----+--+----+---------+
COUNT|id|name|source_id|
+----+--+----+---------+
.2...|11|aaaa|null
+----+--+----+---------+
.2...|12|bbbb|1
+----+--+----+---------+
.3...|15|eeee|2
+----+--+----+---------+
如您所见,结果有两个问题:
- 条目按首次
source_id
出现分组(应为last(最新)) nulls
也被分组(不应该被分组)
我上面描述的任务可以实现吗?我该怎么做?
编辑:
SELECT *,COUNT(id) AS change_count FROM
(SELECT *,(To_days(date_return_due)-TO_DAYS(NOW())) as dayDiff FROM mytable
WHERE owner_id='1'
HAVING dayDiff < 100
ORDER BY date_created DESC) AS newtable
GROUP BY (CASE WHEN source_id IS NULL THEN id ELSE source_id END)
ORDER BY (CASE WHEN source_id IS NULL THEN 1 ELSE 0 END),date_created DESC";