MySQL Merge two queries based on mutual column - mysql

Question

I have two queries that retrieve records from 2 different tables that are almost alike and I need to merge them together.
Both have created_date which is of type datetime and I'm casting this column to date because I want to group and order them by date only, I don't need the time.
First query:
select cast(created_date as date) the_date, count(*)
from question
where user_id = 2
group by the_date
order by the_date;
+------------+----------+
| the_date | count(*) |
+------------+----------+
| 2021-01-02 | 1 |
| 2021-02-10 | 1 |
| 2021-02-14 | 5 | -- this line contains a mutual date
| 2021-03-16 | 1 |
| 2021-03-26 | 3 |
| 2021-03-27 | 23 |
| 2021-03-28 | 5 |
| 2021-03-29 | 1 |
+------------+----------+
Second query:
select cast(created_date as date) the_date, count(*)
from answer
where user_id = 2
group by the_date
order by the_date;
+------------+----------+
| the_date | count(*) |
+------------+----------+
| 2021-02-08 | 2 |
| 2021-02-14 | 1 | -- this line contains a mutual date
| 2021-04-05 | 5 |
| 2021-04-06 | 2 |
+------------+----------+
What I need is to merge them like this:
+------------+---------------+---------------+
| the_date | count(query1) | count(query2) |
+------------+---------------+---------------+
| 2021-01-02 | 1 | 0 | -- count(query2) is 0 bc. it's not in the second query
| 2021-02-08 | 0 | 2 | -- count(query1) is 0 bc. it's not in the first query
| 2021-02-10 | 1 | 0 |
| 2021-02-14 | 5 | 1 | -- mutual date
| 2021-03-16 | 1 | 0 |
| 2021-03-26 | 3 | 0 |
| 2021-03-27 | 23 | 0 |
| 2021-03-28 | 5 | 0 |
| 2021-03-29 | 1 | 0 |
| 2021-04-05 | 0 | 5 |
| 2021-04-06 | 0 | 2 |
+------------+---------------+---------------+
Basically what I need is to have all dates together and for each date to have the corresponding values from those two queries.

Answer 1

try something like this.
SELECT the_date , max(cnt1) , max(cnt2)
FROM (
select cast(created_date as date) the_date, count(*) AS cnt1 , 0 as cnt2
from question
where user_id = 2
group by the_date
order by the_date
UNION ALL
select cast(created_date as date) the_date, 0, count(*)
from answer
where user_id = 2
group by the_date
order by the_date
) as t1
GROUP BY the_date
ORDeR BY the_date;