Tagged articles

NOT EXISTS

2 articles · Page 1 of 1

May 10, 2020 · Databases

Optimizing NOT EXISTS Queries with LEFT JOIN in MySQL: A Performance Comparison

This article examines why NOT EXISTS can perform poorly in MySQL, demonstrates how rewriting the query with a LEFT JOIN dramatically reduces execution time, and explains the underlying indexing and profiling details that affect query efficiency.

LEFT JOINMySQLNOT EXISTS

0 likes · 6 min read

Optimizing NOT EXISTS Queries with LEFT JOIN in MySQL: A Performance Comparison

dbaplus Community

Nov 6, 2019 · Databases

Understanding SQL NULL: Three-Valued Logic, IS NULL vs = NULL, and Common Pitfalls

This article explains the meaning of NULL in SQL, distinguishes the two conceptual types of unknown and not‑applicable, describes three‑valued logic, shows why IS NULL must be used instead of = NULL, and warns about pitfalls such as NOT IN with NULL and improper CASE expressions.

DatabaseIS NULLNOT EXISTS

0 likes · 17 min read

Understanding SQL NULL: Three-Valued Logic, IS NULL vs = NULL, and Common Pitfalls