SQL - 计算计数百分比（列）
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SQL - Calculate percentage on count(column)
提问by Dean Flaherty
I have the following piece of code which counts how many times something appears in the event column.
我有以下一段代码，它计算事件列中出现的次数。
SELECT event, count(event) as event_count
FROM event_information
group by event
event event_count
a 34
b 256
c 45
d 117
e 3
I want to be able to calculate the percentage of each of the rows like so.
我希望能够像这样计算每一行的百分比。
event event_count event_percent
a 34 7.47
b 256 56.26
c 45 9.89
d 117 25.71
e 3 0.66
回答by juergen d
SELECT event,
count(event) as event_count,
count(event) * 100.0 / (select count(*) from event_information) as event_percent
FROM event_information
group by event
回答by Gordon Linoff
Most SQL dialects support ANSI standard window functions. So, you can write the query as:
大多数 SQL 方言都支持 ANSI 标准窗口函数。因此，您可以将查询编写为：
select event, count(*) as event_count,
count(*) * 100.0/ sum(count(*)) over () as event_percent
from event_information
group by event;
Window functions are generally more efficient than subqueries and other methods.
窗口函数通常比子查询和其他方法更有效。
