SQL DAY 10

SQL Day 10: Window Functions, CTEs & Advanced Analytics Welcome to Day 10 of the SQL Masterclass! If there is one lesson that separates junior query-writers from Senior Data Engineers, it is this one. Today, we unlock the most powerful analytical tools in the SQL language. In Hour 1, we break down Window Functions. We will learn how to use the OVER() and PARTITION BY clauses to run heavy aggregations without collapsing our rows like a standard GROUP BY would. We also cover exactly how to build pagination and leaderboards using ROW_NUMBER(), RANK(), and DENSE_RANK(). In Hour 2, we move into script architecture and financial reporting. We ditch messy self-joins and use LAG and LEAD for instant Month-over-Month time-series analysis. We automate our financial grand totals using WITH ROLLUP, clean up nested subqueries using Common Table Expressions (CTEs), and finally, learn how to prevent our scripts from crashing using T-SQL's TRY...CATCH error handling. What you will master in this advanced session: The Window Concept: Aggregating data row-by-row using OVER and PARTITION BY. Advanced Ranking: Using ROW_NUMBER, RANK, and NTILE to group data into quartiles and remove duplicates. Time-Series Analytics: Looking backwards and forwards in your data instantly using LAG and LEAD. Automated Subtotals: Generating hierarchical rollups and grand totals for financial reports. Script Architecture (CTEs): Using the WITH clause to write modular, highly readable, and professional code. T-SQL Error Handling: Using TRY...CATCH to gracefully log errors without corrupting your database state.