一、first()

first(value, time)获取分组内返回时间早的数据
代码如下（示例）：

SELECT
	station_id,
	first( jsondata, dcollectdate )  
FROM
	sc_customer_data 
GROUP BY
	station_id

2. last()

last(value, time)获取分组内返回时间晚的数据

代码如下（示例）：

SELECT
	station_id,
	LAST ( jsondata, dcollectdate )  
FROM
	sc_customer_data 
GROUP BY
	station_id

3.time_bucket()

time_bucket()每隔一段时间进行聚合查询

查询每隔五分钟的后一条数据
SELECT
	time_bucket ( '5 minutes', dcollectdate ) AS TIME,
	LAST ( jsondata, dcollectdate ) 
FROM
	sc_customer_data 
WHERE
	station_id = 'ff1eed991ae90ad3e0c50bf14a0a3c21' 
GROUP BY
TIME 
ORDER BY
	TIME DESC;

 来源 https://blog.csdn.net/qq_38836114/article/details/123739472?ops_request_misc=%257B%2522request%255Fid%2522%253A%2522165234299716782391851447%2522%252C%2522scm%2522%253A%252220140713.130102334.pc%255Fblog.%2522%257D&request_id=165234299716782391851447&biz_id=0&utm_medium=distribute.pc_search_result.none-task-blog-2~blog~first_rank_ecpm_v1~rank_v31_ecpm-30-123739472-null-null.nonecase&utm_term=TimescaleDB&spm=1018.2226.3001.4450

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