[Bug] The calculation logic of the standard deviation aggregation function is incorrect.

[LingweiKuang]

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• I searched in the issues and found nothing similar.

Version

version 1.3.3 (Build: ad95a7e)

Describe the bug and provide the minimal reproduce step

DROP DATABASE root.db0
CREATE DATABASE root.db0

CREATE TIMESERIES root.db0.t1 WITH datatype=INT32;
INSERT INTO root.db0(timestamp, t1) VALUES (1641024000000, 0), (1641024005000, 1);

# query 1
SELECT STDDEV(t1) FROM root.db0 GROUP BY ([1641024000000, 1641024010000),10s);

What did you expect to see?

Query 1 returned result set: 0.5

What did you see instead?

Query 1 returned result set: 0.7071067811865476

Anything else?

In Query 1, we perform a GROUP BY operation on the data of 0 and 1, and calculate the standard deviation of the aggregation result. In principle, the standard deviation should be 0.5, but the result returned by IOTDB is 0.70, which is a significant error. This issue with inaccurate calculations may cause problems for users in high-precision application scenarios.

Are you willing to submit a PR?

• I'm willing to submit a PR!

[LingweiKuang]