假设我有一个包含三个字段的表格:event_name
,event_timestamp
event_result
。每一行都是event_name
发生的事件 event_timestamp
,其中有一些event_result
。例如:
event_name | event_timestamp | event_result
-------------------------------------------
event_a | 2018-04-29 00:00 | result_x1
event_a | 2018-04-29 00:00 | result_x2
event_b | 2018-04-29 00:00 | result_x1
event_a | 2018-04-29 00:00 | result_x3
event_b | 2018-04-29 00:00 | result_x3
现在我需要一个SQL查询来在event_timestamp
的给定范围内为每个 event_name
选择最新 event_timestamp
的行
你会怎么写这样的查询?我想它应该是适用于任何合理的SQL数据库的标准SQL。
答案 0 :(得分:2)
使用subquery
:
select *
from table t
where event_timestamp = (select max(event_timestamp)
from table
where event_name = t.event_name);
而且,一般来说,最有效的方法是使用排名功能(如果支持)
select * from (
select *,
row_number() over (partition by event_name order by event_timestamp desc) Seq
from table t
where event_timestamp between @start and @end
) t
where Seq = 1;
答案 1 :(得分:1)
最便携的解决方案可能是:
SELECT E.*
FROM Event E
INNER JOIN (
SELECT event_name
, MAX(event_timestamp) MAX_DT
FROM Event
WHERE event_timestamp <= @SomeDate
AND event_timestamp > @SomeOtherDate
GROUP BY event_name
) MAXED
ON MAXED.event_name = E.event_name
AND MAXED.MAX_DT = E.event_timestamp
答案 2 :(得分:0)
类似的东西:
SELECT event_name
,MAX(event_timestamp)
FROM myTable
WHERE event_timestamp BETWEEN date1
AND date2
GROUP BY event_name
答案 3 :(得分:0)
您可以使用group by并包含max event_timestamp 在MSSQL中:
select
event_name
, MAX(event_timestamp)
from [table_name]
where event_timestamp between '2018-04-20' and '2018-04-30'
group by event_name
答案 4 :(得分:0)
SELECT * FROM `your_table`
WHERE `event_timestamp` BETWEEN 'your_start_range'AND 'your_end_range'
GROUP BY `event_name`
ORDER BY `event_timestamp` DESC
LIMIT 1;
答案 5 :(得分:0)
此代码适用于ms sql
SELECT *
FROM
(SELECT
*, ROW_NUMBER() OVER(PARTITION BY event_name ORDER BY event_timestamp DESC) AS row_no
FROM Event
WHERE
event_timestamp BETWEEN @BeginDate AND @EndDate) as tbl
WHERE row_no = 1