2.7节遗漏未译

[yukaijian]

2.7. Aggregate Functions最后部分：
Another way to select the rows that go into an aggregate computation is to use FILTER, which is a per-aggregate option:

SELECT city, count(*) FILTER (WHERE temp_lo < 45), max(temp_lo)
FROM weather
GROUP BY city;
city | count | max
---------------+-------+-----
Hayward | 1 | 37
San Francisco | 1 | 46
(2 rows)
FILTER is much like WHERE, except that it removes rows only from the input of the particular aggregate function that it is attached to. Here, the count aggregate counts only rows with temp_lo below 45; but the max aggregate is still applied to all rows, so it still finds the reading of 46.
这部分内容从PG10.0开始就有了，一直未翻译。

[TsinghuaLucky912]

request

已补充

[ChenHuajun]

thanks