Page 17 - SQL

Flawed business data rarely stands out immediately, yet it distorts every analysis built on top of it. Claude helps define validation rules, reliably detect duplicates, systematically identify outliers, and automate data quality reports. This article covers the complete path from the problem class to a built-in quality gate.

Duplicates rarely appear on purpose, they creep in: a missing unique constraint, an import run twice, a race condition under concurrent writes, or a merge of two data sources without reconciliation. Once they are in the database, they distort analytics, bloat joins, and undermine trust in reports. This article systematically shows how to find exact and fuzzy duplicates, how to safely choose which record to keep, and how deletion still works even when other tables reference the duplicates through foreign keys.

A deadlock occurs when two transactions block each other because each is waiting for a resource the other one holds. Consistent lock ordering in application code, short transactions, and robust retry logic prevent most deadlocks before the database ever has to step in.

A deadlock log entry looks like cryptic noise at first glance, but it contains all the information needed to reconstruct the cause precisely. Analyzing deadlocks from logs systematically, instead of dismissing them as rare chance events, reveals the underlying lock order in the code and fixes it permanently instead of just waiting for the next reconnect.