此查询(最小可重现的示例)：
WITH t as (
SELECT 3 id,2 price,0 amount
)
SELECT
CASE WHEN amount > 0 THEN
SUM(price / amount)
ELSE
price
END u_price
FROM t
GROUP BY id,price,amount
在Postgresql 9.4抛出
division by zero
没有SUM就可以了.
这怎么可能？
我喜欢这个问题,我求助于这些
tough guys：
策划者有罪：
A CASE cannot prevent evaluation of an aggregate expression contained
within it,because aggregate expressions are computed before other
expressions in a SELECT list or HAVING clause are considered
更多细节见https://www.postgresql.org/docs/10/static/sql-expressions.html#SYNTAX-EXPRESS-EVAL
