SQL Mastery
Revision Notes Hub

Change table structures safely, understand NULL and constraints, and use UPDATE or DELETE with deliberate filters.

Retrieve the right rows using DISTINCT, WHERE, IN, AND/OR and LIKE; understand exact matches versus patterns.

Understand SQL's logical execution order, handle NULL correctly, aggregate with GROUP BY, and filter groups with HAVING.

Combine related tables with INNER, LEFT, RIGHT, FULL and CROSS JOINs; choose a join based on which rows must remain.

Use self joins, date functions, CASE and STRING_AGG to compare rows and build useful group-level results.

Use CASE inside aggregates, handle strings and NULLs, and combine result sets with UNION, INTERSECT and EXCEPT.

Relate rows within one table, stack report outputs with UNION ALL, create views and enforce relationships with foreign keys.

Break complex questions into subqueries and CTEs; derive intermediate results and use them in filters or calculations.

Use ROW_NUMBER, RANK, DENSE_RANK, LEAD and LAG to number, compare and analyse rows within partitions.

Calculate running and rolling totals with window frames; understand OVER, ORDER BY, ROWS, RANGE and value functions.

Encapsulate reusable logic in stored procedures and functions, use parameters and messages, and reshape data with PIVOT.

Apply correlated subqueries and EXISTS, update or delete through related tables, manage permissions and transactions, and UNPIVOT.

Understand clustered and nonclustered indexes, B-tree seeks, lookup costs and INCLUDE; identify and remove duplicate rows.

Learn Tableau's dimensions, measures, live connections and extracts; build a worksheet from a data source and relationships.

Work through a credit-card transaction project: explore data, rank results, calculate contribution, cumulative spend and growth.

Diagnose duplicate rows and join multiplication, check key uniqueness, handle date-range joins and understand import issues.

Strengthen window functions, CTEs and GROUP BY through tricky questions; practise reasoning, debugging and career-focused learning.