regr_sxy aggregate function
Applies to: 
Databricks SQL Databricks Runtime 11.3 LTS and above
Returns the sum of products of yExpr and xExpr calculated from values of a group where xExpr and yExpr are NOT NULL.
Syntax
regr_sxy( [ALL | DISTINCT] yExpr, xExpr) [FILTER ( WHERE cond ) ]
This function can also be invoked as a window function using the OVER clause.
Arguments
yExpr: A numeric expression, the dependent variable.xExpr: A numeric expression, the independent variable.cond: An optional Boolean expression filtering the rows used for the function.
Returns
The result type is a DOUBLE.
Any nulls within the group are ignored. If a group is empty or consists only of nulls, the result is NULL.
If DISTINCT is specified, the result is computed after duplicates are removed.
regr_sxy(y, x) is a synonym for regr_count(y, x) * covar_pop(y, x).
Examples
> SELECT regr_sxy(y, x) FROM VALUES (1, 2), (2, 3), (2, 3), (null, 4), (4, null) AS T(y, x);
0.6666666666666666