Increment Row Index And Union With Other Tables On Dynamic Dates - mysql

Question

Question:
I looked at various other examples to increment over rows, but all resulted in the same wrong output. The problem which I encountered was that my code did not successfully increment over rows to build a correct index per new row in the result-set per episode (highlighted in red below).
My first try was:
SET #ep_1 = "Peaky Blinders";
SET #curRow_1 = 0;
SELECT
DATE_FORMAT(created_at, "%Y%m%d") AS year_month_day,
#curRow_1 := #curRow_1 + 1 AS row_number,
#ep_1 AS episode_title,
COUNT(id) AS episode_plays
FROM netflix.episode_plays
WHERE
episode_id = "xyz"
AND created_at >= "2019-07-01" AND created_at <= "2019-07-07"
GROUP BY 1
Other than the rows not incrementing correctly; I also got the following error when I tried setting some variables in the beginning of my code:
Error running query: Illegal mix of collations (utf8_unicode_ci,IMPLICIT) and (utf8_general_ci,IMPLICIT) for operation '='
(Note: I have no affiliation with Netflix, I just used Netflix dummy data to answer my question)

Answer 1

I broke down my question in various sections and got to the final answer below.
The most important part was to add the initial result-sets into a subqueries, and thereafter select the data from tables x1,x2, etc.
The second part of the question was, how to combine multiple datasets together (in my case: how do one not only do it for one specific netflix episode, but multiple episodes)? I settled on the UNION ALL - clause.
In the first iteration I tried hard-coding the dates, and thereafter found the INTERVAL-function very helpful.
Finally, the unicode-error I fixed by adding COLLATE utf8_unicode_ci after setting my variables.
If you find mistakes in my code or have any other suggestions, please feel free to suggest them.
-- SET DATA
-- variables for table x1
SET #ep_1 = "Peaky Blinders" COLLATE utf8_unicode_ci;
SET #id_1 = (SELECT id FROM netflix.episodes WHERE episode_title = #ep_1);
SET #date_1 = (SELECT created_at FROM netflix.episodes WHERE episode_title = #ep_1);
SET #curRow_1 = 0;
-- variables for table x2
SET #ep_2 = "Brooklyn Nine-Nine" COLLATE utf8_unicode_ci;
SET #id_2 = (SELECT id FROM netflix.episodes WHERE episode_title = #ep_2);
SET #date_2 = (SELECT created_at FROM netflix.episodes WHERE episode_title = #ep_2);
SET #curRow_2 = 0;
-- QUERY DATA
SELECT
x1.year_month_day,
#curRow_1 := #curRow_1 + 1 AS row_number,
x1.episode_title,
x1.episode_plays
FROM (
SELECT
DATE_FORMAT(created_at, "%Y%m%d") AS year_month_day,
#ep_1 AS episode_title,
COUNT(id) AS episode_plays
FROM netflix.episode_plays
WHERE
episode_id = #id_1
AND created_at >= #date_1 AND created_at <= DATE_ADD(#date_1 , INTERVAL 7 DAY)
GROUP BY 1) x1
UNION ALL
SELECT
x2.year_month_day,
#curRow_2 := #curRow_2 + 1 AS row_number,
x2.episode_title,
x2.episode_plays
FROM (
SELECT
DATE_FORMAT(created_at, "%Y%m%d") AS year_month_day,
#ep_2 AS episode_title,
COUNT(id) AS episode_plays
FROM netflix.episode_plays
WHERE
episode_id = #id_2
AND created_at >= #date_2 AND created_at <= DATE_ADD(#date_2 , INTERVAL 7 DAY)
GROUP BY 1) x2