Step-by-step tutorials on Excel, Python, databases, and developer tools
132 articles
Getting a #VALUE! error from XLOOKUP when your return array spans multiple columns? This is a common spill behavior trap. Learn exactly why it happens and how to fix it in a few keystrokes.
COUNTIFS applies AND logic by default, so combining OR conditions inside one formula silently undercounts your data. Here's exactly why it breaks and four reliable patterns to fix it.
Your INSERT ... ON CONFLICT DO UPDATE is firing on every row, stamping updated_at even when nothing changed. Here's why that happens and exactly how to fix it with a conditional DO UPDATE clause.
XLOOKUP silently returns wrong values when your search array contains merged cells — not an error, just the wrong answer. Here's exactly why it happens and how to fix it for good.
Your INDEX MATCH formula works fine on a single column but throws #VALUE! the moment you extend it across multiple columns. Here's exactly why that happens and the precise fixes to make it work.
VLOOKUP always returns the first match it finds — so when your lookup table has duplicate keys, you get the wrong value with no error to warn you. Here's how to diagnose the problem and fix it for good.
AVERAGEIFS throws #DIV/0! and your named range looks perfectly fine — so what's going wrong? The culprit is usually a size mismatch or scope conflict that Excel silently fails on. Here's how to diagnose and fix it.
Your PostgreSQL rank is returning unexpected numbers when multiple rows share the same value in a partition. Here's exactly why RANK(), DENSE_RANK(), and ROW_NUMBER() behave differently on ties — and how to pick the right one.
Your SUMIF looks right, your criteria is correct, but the total is off — and the only thing that changed was filtering or hiding some rows. Here's exactly why SUMIF ignores your hidden-row expectations and how to fix it.
Running pd.merge() and getting way more rows than expected? When join keys aren't unique on both sides, Pandas does a cartesian product on matches — and the result can silently balloon your DataFrame. Here's how to diagnose and fix it.
COUNTIFS with date ranges looks right but counts wrong — a frustrating bug that hides in plain sight. Learn exactly why Excel misreads your date criteria and the fixes that actually work.
Your INDEX MATCH formula looks perfect but keeps throwing #N/A — and the culprit is a merged cell in your lookup range. Here's exactly why this breaks and how to fix it without losing your layout.