Calculates the population covariance between two data columns. The population covariance measures the degree to which two variables vary together. Calculates the amount `Σ((x - x̅)^2) / n`, where `n` is the sample size and `x̅`is the average value of `x`.
-`x`: The first data column. [Numeric](../../../native-protocol/columns.md)
-`y`: The second data column. [Numeric](../../../native-protocol/columns.md)
**Returned value**
Returns an integer of type `Float64`.
**Implementation details**
This function uses a numerically unstable algorithm. If you need numerical stability in calculations, use the slower but more stable [`varPopStable` function](#varPopStable).
Calculates population covariance between two data columns using a stable, numerically accurate method to calculate the variance. This function is designed to provide reliable results even with large datasets or values that might cause numerical instability in other implementations.
**Syntax**
```sql
covarPopStable(x, y)
```
**Parameters**
-`x`: The first data column. [String literal](../syntax#syntax-string-literal)
-`y`: The second data column. [Expression](../syntax#syntax-expressions)
**Returned value**
Returns an integer of type `Float64`.
**Implementation details**
Unlike [`varPop()`](#varPop), this function uses a stable, numerically accurate algorithm to calculate the population variance to avoid issues like catastrophic cancellation or loss of precision. This function also handles `NaN` and `Inf` values correctly, excluding them from calculations.