[英]SQL: How to select one row per day
I have a database that has a row entry for every minute (86,000 values per day) and I am trying to write PHP to select only one row per day. 我有一个数据库,该数据库每分钟都有一行条目(每天86,000个值),并且我试图编写PHP以每天仅选择一行。 I have a column "timestamp" that has the current timestamp in regular format (2017-12-09 06:49:02).
我有一列“时间戳”,该列具有常规格式的当前时间戳(2017-12-09 06:49:02)。
Does anyone know how to write a select statement to do what I am trying to do? 有谁知道如何写一个选择语句来做我想做的事情?
Example output: 输出示例:
2017-12-09 06:49:02, datavalue
2017-12-10 06:49:02, datavalue
2017-12-11 06:49:02, datavalue
2017-12-12 06:49:02, datavalue
Here is one method: 这是一种方法:
select t.*
from t join
(select min(t2.timestamp) as min_timestamp
from t t2
group by date(t2.timestamp)
) t2
on t.timestamp = t2.min_timestamp;
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