Log in Start learning

Module 2

SQL

Retrieve, combine and summarise data in relational databases — from first SELECT to window functions and query performance.

Difficulty:All beginner intermediate advanced expert

Joins and Combining Data

Joining tables correctly and avoiding double counting.

Joins

✓Joins — combining tables without double countingINNER, LEFT, RIGHT, FULL and self joins, multi-table joins, and the fan-out problem that silently inflates totals.Intermediate60 min

Subqueries, CTEs and set operations

✓Subqueries, CTEs and UNIONBuild queries in steps with subqueries and common table expressions, compare rows to their own group with correlated subqueries, and stack results with UNION.Intermediate50 min

Functions

Dates, strings and numbers.

Date, string and numeric functions

✓Date, string and numeric functionsBucket dates into months and weeks, compute durations, clean text and round numbers — with notes for PostgreSQL and SQL Server.Intermediate45 min

Performance and Data Quality

Indexes, execution plans, validation and reconciliation.

Validation and reconciliation

✓Data validation and reconciliation in SQLProve that your numbers are right before anyone else finds out they are wrong — profiling, integrity checks and reconciliation to independent totals.Intermediate45 min