SQL — Tag - mteq.pro

Apr 17, 2026

SQL NULL Handling: COALESCE, NULLIF, and CASE

NULL is not zero and not empty. It means the value is unknown. This post explains how NULL behaves in SQL, how to test for it, and how to handle it safely using COALESCE, NULLIF, and CASE.

Data Engineering #SQL

Apr 17, 2026

SQL Set Operators: UNION, INTERSECT, and EXCEPT

Set operators let you combine the results of two queries into one. This post explains how UNION, UNION ALL, INTERSECT, and EXCEPT work, when to use each one, and how they apply to real data engineering tasks.

Data Engineering #SQL #Set Operators

Apr 16, 2026

How SQL Indexes Work (And How to Optimize Them)

Without an index, every query reads the entire table. This post explains how indexes work, when to create them, how SARGability breaks index usage, and how to read a query plan to confirm performance improvements.

Data Engineering #SQL #SQL Indexes #Query Optimization #SARGability

Apr 14, 2026

Which Rows Survive a SQL Join?

SQL JOINs do more than combine tables. They decide which rows survive, which become NULL, and which disappear entirely. This post explains INNER, LEFT, RIGHT, FULL, CROSS, and SELF JOINs with practical examples and mental models.

Data Engineering #SQL #SQL Joins