sql：列中类型的百分比

Question

I'm trying to get percentage of missed calls for each user, so I used the following sql query:

select distinct a__contact
       , count (case when a__type = 'missed' 
                     then 1 else 0 end) / count(*) * 100 
                                                  as "percentage of missed calls"

from table
group by 1

However, for each user I got 100 which do not seem to be correct output at all. Could someone help me to identify the error in my query? thank you so much!

Answer 1

Here is a simpler way to express the logic you want:

select a__contact,
       avg(case when a__type = 'missed' then 100.0 else 0 end) as percentage_missed_calls
from table
group by 1;

Your version is failing because you are using count() in the numerator. You really intend sum() . count() counts the number of non- NULL values and both "1" and "0" are non- NULL .