Field note · January 25, 2026
Correction: Slowly changing dimension, type 2
The page claimed more than it should have. What it says now, and where the pattern stops applying.
Sharpened the wording on Slowly changing dimension, type 2 after someone pointed out it was overstated.
The original read as though the pattern always applies. It does not. Keep every version of a row so "what was true in February" stays answerable after March changes it.
What it should have said — and now does — is where it stops applying. Every technique has a range of validity, and a pattern library that states rules without stating their limits produces exactly the cargo-culting it was meant to prevent.
The revised page names the case where the simple version is fine, so you are not paying the cost of the careful version on a table with four rows.
Corrections go in the page, with a note about what changed. No silent edits. The course will contain errors — it is thirty-six lessons about a field where the standard advice is frequently wrong — and the only defensible approach is to fix them visibly.
The repository takes issues, and several pattern pages are sharper than what we shipped because someone argued.