Hard
SQL-O10sqlDenormalise A Hot Counter
Problem
`SELECT COUNT(*) FROM likes WHERE post_id = ?` is now hot and slow at 100M rows. The post page hits it on every render. Propose a denormalisation strategy and write the trigger / atomic SQL that maintains it.
Input
Conceptual + SQL.
Output
Counter table + trigger
Constraints
—
Sample input
—
Sample output
Maintain `posts.likes_count` directly via a trigger or atomic UPDATE on insert/delete.
Explanation
Reads outweigh writes → store the count.
optimisationdenormalisationcounters@Twitter
Visible test cases
in: explain
out: ok
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