regr_sxx
regr_sxx 介绍
regr_sxx(y, x) - 对于组中的非空值对，返回 REGR_COUNT(y, x) * VAR_POP(x)，其中 y 是因变量，x 是自变量。
Examples:
> SELECT regr_sxx(y, x) FROM VALUES (1, 2), (2, 2), (2, 3), (2, 4) AS tab(y, x);
2.75
> SELECT regr_sxx(y, x) FROM VALUES (1, 2), (2, null), (2, 3), (2, 4) AS tab(y, x);
2.0
> SELECT regr_sxx(y, x) FROM VALUES (1, 2), (2, null), (null, 3), (2, 4) AS tab(y, x);
2.0Since: 3.4.0