Cold Case~65min
The Algorithm That Forgot
The recommendation engine stopped serving content to users aged 45 and above. Their CTR dropped to zero. No one filed a bug report. The algorithm was retrained 6 weeks ago.
Tables you'll query
usersrecommendationscontent_viewsmodel_versions
What you'll learn
Window FunctionsCTEs (WITH clause)JOINsSubqueriesAggregations & GROUP BY