Learn SQL time series analysis with real examples: date truncation, filling gaps with a full date series, moving averages, period-over-period comparisons, and gaps-and-islands.

SQL vs NoSQL explained for data scientists: how relational and non-relational databases actually differ, when each wins, and why SQL remains the non-negotiable skill.

SQL Query Optimization: 10 Techniques That Work (2026) Home / Data Science / SQL for Data Science / Query Optimization ⚡ SQL Cluster — 10 of 15 · Advanced SQL Query Optimization: 10 Techniques That Work (2026) A query returns instantly against 10,000 rows in a dev database. The same query, unchanged, takes 45 seconds

Learn SQL window functions with real examples: ROW_NUMBER, RANK vs DENSE_RANK, LAG and LEAD, running totals, PARTITION BY, and the top-N-per-group pattern.

Learn SQL subqueries and CTEs with real examples: scalar and correlated subqueries, EXISTS vs IN, the WITH clause, recursive CTEs, and when each one is the better choice.

A complete guide to SQL aggregate functions: SUM, COUNT, AVG, MIN, MAX, how each treats NULLs, COUNT DISTINCT, conditional aggregation, and the AVG NULL trap that skews reports.

Learn SQL JOINs with real examples: INNER, LEFT, RIGHT, and FULL joins, finding unmatched rows, the join fan-out trap that silently inflates aggregates, and multi-table joins.

SQL GROUP BY and HAVING: Full Guide (2026) Home / Data Science / SQL for Data Science / GROUP BY & HAVING 📊 SQL Cluster — 5 of 15 · Intermediate SQL GROUP BY and HAVING: Full Guide (2026) On an older MySQL setup with a relaxed SQL mode, a query like SELECT customer_id, name,

SQL Data Types Explained (2026) Home / Data Science / SQL for Data Science / Data Types 📦 SQL Cluster — 4 of 15 SQL Data Types Explained (2026) A finance table stores prices as FLOAT. Nine months and a few million rows later, the total revenue report is off by $340 — not from

SQL ORDER BY and LIMIT: Sorting Query Results (2026) Home / Data Science / SQL for Data Science / ORDER BY & LIMIT ⇅️ SQL Cluster — 3 of 15 SQL ORDER BY and LIMIT: Sorting Query Results (2026) A “top 10 customers by revenue” report gets built with LIMIT 10 and no ORDER BY