Careers & Skills
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TutorialCareers & Skills · TutorialMost Analytics Bugs Are Data Bugs. Five Checks That Catch Them Before the Meeting.
Five validation checks every analyst should run before trusting a table: duplicates, NULL key columns, out-of-range values, cross-field arithmetic, orphan references. Tested on a 2,010-row orders table with 50 planted defects; the checks flagged 51 rows, and the misses are as instructive as the catches.
Ibrahim Denis Fofanah·Oct 11, 2026·8 min
TutorialCareers & Skills · TutorialWindow Functions Are SQL's Most Underused Feature. Five Patterns Cover Nearly Everything.
Five window-function patterns that cover most analytics SQL: dedupe with ROW_NUMBER, top-N per group with RANK, period comparisons with LAG, running totals with explicit frames, bucketing with NTILE. Every query ran and its output is shown; a 200,000-row timing test puts the window function at 0.46s against 5.92s for the equivalent self-join on 5,000 rows.
Ibrahim Denis Fofanah·Oct 6, 2026·8 min