In data analysis, small misunderstandings can lead to big reporting errors. One of the most common one is confusing null with unknown. What 'Null' means: In SQL, Null means, 'missing' or 'no value'. It does not mean: 0 blank Unknown False It simply means the value does not exist. For example: SELECT COUNT(*) FROM referrals WHERE cause_of_death IS NULL; This tells us how many are missing information - not how many are unknown. What 'Unknown' means: Unknown is a valid category

WHY ANALYSTS NEED WINDOW FUNCTIONS? Before we deep dive into what a window function is, the syntax and how to write it, let us understand why we even need a window function. When you work for a company, as an analyst, you’re constantly asked things like: “How does this row compare to others?” “What has changed since last week?” “What’s the running total?” “Who’s top-N within each group?” “What’s this user’s previous / next event?” A classic SQL ( GROUP BY ) can’t answer thos