try_avg
try_avg 介绍
try_avg(expr) - 从一组值中计算平均值，如果发生溢出，则结果为null。
Examples:
> SELECT try_avg(col) FROM VALUES (1), (2), (3) AS tab(col);
2.0
> SELECT try_avg(col) FROM VALUES (1), (2), (NULL) AS tab(col);
1.5
> SELECT try_avg(col) FROM VALUES (interval '2147483647 months'), (interval '1 months') AS tab(col);
NULLSince: 3.3.0