[HY000][1111] Invalid use of group function - mysql

Question

I have searched a lot ,but none of other questions with error 1111 solves my problem.
My needs are to count the distinct phone number of some id
The following code works:
SELECT
a.id_borrow_application,
count(DISTINCT c.phone_no) CVG_CALL_OUT_COUNTS_6M
FROM t_snow_borrow_application_id a
JOIN t_snow_call_mobile b
JOIN t_snow_call_record_201612 c ON
(
a.id_borrow_application = b.id_borrow_application
AND b.id = c.id_call_mobile
)
WHERE c.call_type = 0
GROUP BY a.id_borrow_application;
But when I want to write 4 similar queries together,the error in title
happens.
[HY000][1111] Invalid use of group function
SELECT
a.id_borrow_application,
sum(CASE WHEN call_type = 0
THEN count(DISTINCT c.phone_no)
ELSE 0 END) CVG_CALL_OUT_COUNTS_6M,
sum(CASE WHEN call_type = 0 AND c.days <= 30
THEN count(DISTINCT c.phone_no)
ELSE 0 END) CVG_CALL_OUT_COUNTS_1M,
sum(CASE WHEN call_type = 1
THEN count(DISTINCT c.phone_no)
ELSE 0 END) CVG_CALL_IN_COUNTS_6M,
sum(CASE WHEN call_type = 1 AND c.days <= 30
THEN count(DISTINCT c.phone_no)
ELSE 0 END) CVG_CALL_IN_COUNTS_1M
FROM t_snow_borrow_application_id a
JOIN t_snow_call_mobile b
JOIN t_snow_call_record_201612 c ON
(
a.id_borrow_application = b.id_borrow_application
AND b.id = c.id_call_mobile
)
GROUP BY a.id_borrow_application;
Do I have to write 4 queries?

Answer 1

You are nesting aggregate function which is not allowed in MySQL.
You don't actually need the sum function for count distinct phone_nos for different conditions. Take the count (distinct outside the case and remove sum function and else clause of the case.
Try this:
select a.id_borrow_application,
count(distinct case when call_type = 0 then c.phone_no end) CVG_CALL_OUT_COUNTS_6M,
count(distinct case when call_type = 0
and c.days <= 30 then c.phone_no end) CVG_CALL_OUT_COUNTS_1M,
count(distinct case when call_type = 1 then c.phone_no end) CVG_CALL_IN_COUNTS_6M,
count(distinct case when call_type = 1
and c.days <= 30 then c.phone_no end) CVG_CALL_IN_COUNTS_1M
from t_snow_borrow_application_id a
join t_snow_call_mobile b
join t_snow_call_record_201612 c on (
a.id_borrow_application = b.id_borrow_application
and b.id = c.id_call_mobile
)
group by a.id_borrow_application;