Comments - STDDEV_SAMP
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Beware using this function in a view under MariaDB 10.2 up to latest version.
When creating views, those versions erroneously convert any call to STDDEV_SAMP to STD (a shortcut to STDDEV_POP). Since those functions do not behave the same, you will likely have incorrect calculations in those views.
There is a workaround: use SQRT(VAR_SAMP(expr)) instead of STDDEV_SAMP(expr).
Reference: https://jira.mariadb.org/browse/MDEV-19071
GR.