Analytic REGR_* functions and COVAR_POP return internval server error in combination with UNION ALL

In some cases, using one of the REGR_* functions or COVAR_POP as an analytic function together with an UNION ALL expression can lead to an internal server error:

SELECT
    REGR_SLOPE(a,b) over()
FROM
    (SELECT 1 as a, 2 as b UNION ALL SELECT 2 as a, 3 as b)

Replace the REGR_* and COVAR_POP calls with the definitions from the documentation. For example:

SELECT
        ((SUM(a*b) over() - (SUM(a-a+b) over() * SUM(b-b+a) over()) / COUNT(a+b) over()) / COUNT(a+b) over()) / VAR_POP(b) over()
FROM
    (SELECT 1 as a, 2 as b UNION ALL SELECT 2 as a, 3 as b)

These situations will no longer lead to an internal server error.