All Articles & Tutorials
Explore practical guides, step-by-step masterclasses, and foundational definitions across AI, SQL, and data systems — written in plain, human English.
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SQL Tutorial 9: Views and Indexes
Reuse logic with views and speed lookups with indexes on everyday customer and order queries. Learn what each database object is for, how teams share meaning safely, and…
SQL Tutorial 8: Modifying Data with SQL
Change data safely with INSERT, UPDATE, and DELETE on the customers and orders toy schema. Practice row adds, targeted edits, and careful deletes, plus a light take on…
SQL Tutorial 7: Subqueries in SQL
Subqueries nest one query inside another so you can filter and shape results with answers from other answers. Learn scalar, IN, EXISTS, and derived tables on the customers…
SQL Tutorial 6: Joins in SQL
Connect customers to orders with INNER and LEFT joins, using keys on purpose. Learn how join grain can explode row counts, when not to join, and how to…
SQL Tutorial 5: Aggregate Functions and Grouping Data
Turn rows into summaries with COUNT, SUM, AVG, MIN, and MAX. Group with GROUP BY, and learn when HAVING filters groups while WHERE filters rows, so your totals…
