Fix reports screen times out on larger sites

[m1r0]

Resolves #7857
Resolves SEN-23
Probably resolves #4962
Relates to #7858

Proposed Changes

• The PR fixes a slow query on the reports screen that causes a timeout on bigger sites. The performance increase is more than 10-fold.

Testing Instructions

1. Have the Query Monitor plugin installed.
2. Go to Sensei LMS > Reports
3. Look for the query in the screenshot below and compare it trunk.
4. Make sure the listed users and last activity dates are still the same as in trunk
5. Make sure the "Last Activity" date filter still works as before.
6. Make sure the "Last Activity" table sorting still works as before.
7. Make sure the "Export all rows" still works as before.

Before	After

Pre-Merge Checklist

• PR title and description contain sufficient detail and accurately describe the changes
• Adheres to coding standards (PHP, JavaScript, CSS, HTML)
• All strings are translatable (without concatenation, handles plurals)
• Follows our naming conventions (P6rkRX-4oA-p2)
• Hooks (p6rkRX-1uS-p2) and functions are documented
• New UIs are responsive and use a mobile-first approach
• Code is tested on the minimum supported PHP and WordPress versions

[Copilot]

Pull Request Overview

This PR optimizes a slow query on the Sensei LMS reports screen that was causing timeouts on larger sites. The optimization converts a correlated subquery into a LEFT JOIN with GROUP BY, which significantly improves query performance by eliminating the need to execute the subquery for each user row.

Key Changes:

• Replaced a correlated subquery with a LEFT JOIN to fetch last activity dates more efficiently
• Removed the USE INDEX hint that is no longer needed with the new query structure

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
includes/reports/overview/data-provider/class-sensei-reports-overview-data-provider-students.php	Refactored the SQL query to use LEFT JOIN instead of a correlated subquery for better performance
changelog/fix-slow-query-on-reports-screen	Added changelog entry documenting the query optimization fix

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[m1r0]

@donnapep, if you have the opportunity, could you please give this one a look? 🙏

[m1r0]

It was confirmed that this is fixed. 🚀