🗃️
SQL
SQL for Data Engineers
Joins, window functions, CTEs, stored procedures, indexes, transactions, MERGE, and every SQL concept you need.
15 in-depth tutorials
How SQL executes: FROM, WHERE, GROUP BY, HAVING, SELECT, ORDER BY — the real execution order.
02GROUP BY, HAVING & CASE WHEN
Master SQL aggregations with the post office analogy. GROUP BY rules, COUNT/SUM/AVG/MIN/MAX with NULL behavior, WHERE vs HAVING, CASE WHEN in SELECT/WHERE/ORDER BY/aggregations (pivot pattern), COALESCE, NULLIF…
Master all subquery types with the research analogy. WHERE/FROM/SELECT subqueries, correlated subqueries with step-by-step row execution, EXISTS and NOT EXISTS, the same question solved five ways (JOIN, IN, EXISTS…
The complete SQL function reference for data engineers. 50+ functions organized by category: string (TRIM, CONCAT, REPLACE, SUBSTRING, STUFF, STRING_AGG), date (DATEDIFF, DATEADD, DATEPART, EOMONTH, FORMAT), numeric…
Master every SQL join type with visual diagrams and real examples. Covers INNER, LEFT, RIGHT, FULL OUTER, CROSS, and SELF joins, plus ON vs WHERE, CTEs with joins, performance tips, and interview questions.
Master SQL window functions with real examples. Covers ROW_NUMBER, RANK, DENSE_RANK, NTILE, LAG, LEAD, running totals, moving averages, frame clauses, and the most common interview questions.
Master SQL CTEs and subqueries. Learn when to use each, how to chain multiple CTEs, recursive CTEs for hierarchies, deduplication patterns, and real-world data engineering examples.
The complete DDL, DML, and constraints guide. CREATE TABLE with all data types, every constraint explained (PK, FK, UNIQUE, CHECK, DEFAULT, NOT NULL, composite keys), CASCADE options, ALTER TABLE, DROP vs TRUNCATE vs…
Master SQL performance with the book index analogy. Table scan vs index seek, clustered vs non-clustered indexes, composite indexes with leftmost prefix rule, covering indexes with INCLUDE, reading execution plans…
10Views, Temp Tables & Variables
Views, temp tables, table variables, and CTEs compared: scope, persistence, and performance.
11Stored Procedures & Triggers
Automate SQL with stored procedures, functions, and triggers. Procedures with input/output parameters, TRY/CATCH error handling, our pipeline logging procedure. Scalar functions and table-valued functions with use cases.
Database design from both sides. Normalization: 1NF (atomic values), 2NF (no partial dependencies), 3NF (no transitive dependencies) with real examples.
Complete your SQL toolkit. UNION vs UNION ALL vs INTERSECT vs EXCEPT with playlist analogy, SET operations rules, four real-world patterns (multi-source combine, missing records, reconciliation, categorized union).
Master SQL transactions with six real-world scenarios. ACID properties explained with ATM, chess, fitting room, and notary analogies.
15SQL Interview Practice (20 Qs)
20 real SQL interview problems with step-by-step thinking process and solutions.