问题描述
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,但例外:
I'd like to select all entries, with an exception:
- 所有带有
source_id == somevalue(not null)
的条目均应分组 此后应该存在带有 - 最后一个条目
source_id == null
的- all entries with
source_id == somevalue(not null)
should be grouped - last entry with
source_id == null
should exist afterwards
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,我已经完成了此操作(注意:"change_count" = COUNT):
So far I've done this (note: "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
这就是我得到的:
+----+--+----+---------+
COUNT|id|name|source_id|
+----+--+----+---------+
.2...|11|aaaa|null
+----+--+----+---------+
.2...|12|bbbb|1
+----+--+----+---------+
.3...|15|eeee|2
+----+--+----+---------+
您可以看到结果有两个问题:
As you can see the result has 2 problems:
- 条目按第一个
source_id
出现分组(应为最后(最新)) -
nulls
也已分组(不应分组)
- entries are grouped by first
source_id
occurrence (should be last(latest)) nulls
are also grouped (shouldn't be grouped)
我上面描述的任务可以实现吗?我该怎么办?
Is the task that I've described above achievable? How do I do it?
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";
推荐答案
我认为以下内容可以满足您的需求:
I think the following does what you want:
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
它执行条件group by
,因此不会将NULL源ID分组.然后使用order by
中的逻辑将它们置于最后.
It does a conditional group by
so the NULL sourceids will not be grouped. It then puts them last using logic in order by
.
我不明白您最后一次发生的意思.现在我想知道了:
I didn't understand what you meant by last occurrence. Now I think I do:
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).
This joins in the information from the latest record (based on highest id).
这篇关于按非空值分组的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持!