#sql

Problem Description The table tb_healthy records the medical history of patients; each...

Our admin overview used to fire fifteen parallel counts at a five-connection pool. It is now one statement, a 30 second per-process cache, and a product count read from pg_class rather than counted.

A history list needs a score and a caption per row. The rows that hold them also hold every answer the candidate typed, so the select reads two values out of two jsonb columns and leaves the rest in the database.

DBeaver & SQL Summary Learning Notes A step-by-step guide using the Hospital Database...

Once you're collecting LLM answers daily and scoring them for brand mentions, someone will ask for a...

What happens when two users try to update the same database row at exactly the same time? Without...

To join several rows into one string per group in MySQL, use GROUP_CONCAT() with GROUP BY. The order...

Design a recommendation system: the ML system design interview walkthrough The request to...

Design object storage (Amazon S3): the system design interview walkthrough The request to...

Design a distributed job scheduler: the system design interview walkthrough The request to...

Why a table purged by 99% still costs a full scan exactly what it did when it was full: the high-water mark, why DELETE never lowers it, how to find bloated tables from DBA_TABLES, and how SHRINK SPACE or MOVE ONLINE fixes it — with a lab where the same scan costs 6,074 consistent gets before the delete, 6,074 after it, and 64 after the shrink.

PCAD-31-02 has 48 items and 30 come from data prep and Python/SQL. One runnable script: pandas checks, sqlite3 placeholders, read_sql_query.