1683. Invalid Tweets
Question:

Solution:
select
tweet_id
from Tweets
where length(content) > 15
1693. Daily Leads and Partners
Question:

Solution:
select
date_id,
make_name,
count(distinct lead_id) as unique_leads,
count(distinct partner_id) as unique_partners
from DailySales
group by 1,2
1699. Number of Calls Between Two Persons
Question:

Solution:
select
person1,
person2,
sum(calls) as call_count,
sum(duration) as total_duration
from (
select
from_id as person1,
to_id as person2,
1 as calls,
duration
from Calls
where from_id < to_id
union all
select
to_id as person1,
from_id as person2,
1 as calls,
duration
from Calls
where to_id < from_id
) c
group by 1,2