SQL for Testers
SQL tutorials for testers: SELECT, joins, DDL and DML, subqueries, transactions and test data checks.
SQL Query Anti-Patterns: Non-Sargable Queries, N+1, Cartesian Joins and SELECT *
SQL anti-patterns that slow queries or break results: non-sargable predicates, the N+1 problem, Cartesian explosions, SELECT * and reading EXPLAIN plans.
SQL UPSERT, MERGE, LATERAL Joins and Materialized Views
UPSERT in MySQL and PostgreSQL, MERGE in SQL Server and Oracle, LATERAL joins and CROSS APPLY for top-N per row, and materialized views with refresh strategies.
SQL for Data Warehousing: SCD Types 1, 2, 3, Star vs Snowflake Schema, ROLLUP and CUBE
Data warehouse SQL: slowly changing dimensions (SCD Type 1, 2, 3), OLTP vs OLAP, star vs snowflake schema, and ROLLUP, CUBE and GROUPING SETS.
SQL for Data Analytics: KPI, Retention, Cohort and Funnel Queries
Analytics SQL with examples: KPI queries, day-1 and day-7 retention, cohort analysis, conversion funnels, and monthly active users (MAU).
SQL Gaps and Islands: Consecutive Days, Streaks and Missing Values
Solve SQL gaps and islands problems: consecutive login streaks with the ROW_NUMBER trick, missing IDs and dates in a sequence, and longest winning streaks.