ClickHouse/docs/en/sql-reference/aggregate-functions/reference/varsamp.md

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varSamp

Calculates the amount Σ((x - x̅)^2) / (n - 1), where n is the sample size and x̅is the average value of x.

It represents an unbiased estimate of the variance of a random variable if passed values form its sample.

Returns Float64. When n <= 1, returns +∞.

!!! note "Note" This function uses a numerically unstable algorithm. If you need numerical stability in calculations, use the varSampStable function. It works slower but provides a lower computational error.