题解 | #只有我一开始计数用的是 count(age)吗#
select
case when age<20 then '20以下'
when age between 20 and 50 then '20-50'
when age>50 then '50以上'
else '未填写'
end as age_group ,
count(customer_id) as user_count
from customers_info
group by age_group
说来惭愧，计数count（age）,得到的结果是0 ，null不计数，尴尬
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