One query running for all the pages and making many them load slow for large data

[Imran92]

Steps to Reproduce

1. Create a large number of courses, and lessons with many students enrolled
2. Browse the Reports pages (or any other page)
3. Monitor the queries generated
4. See a query getting generated for all of them, making many of them load slow (As attached in the screenshot below)

Screenshot / Video

This query adding more than two seconds to the loading time of Students and Courses pages under Reports. For ~3 Courses, 300 lessons each and ~1200 students enrolled to all of them. The page takes about 4 seconds to load, and this query is responsible for half of it.

[lkraav]

Can you also run an EXPLAIN ... statement on that query and paste the result, for example via wp db cli.

Related: https://dba.stackexchange.com/questions/184685/why-is-count-slow-when-explain-knows-the-answer

[donnapep]

@m1r0 Curious if this issue was fixed by #7859?

[m1r0]

Not sure if that fixed it, but it's no longer reproducible.