J
jeremy
6 minutes
Wrapping a Column in a Function Puts Its Index Out of Reach
Sits on the index-structure and selectivity nodes and explains the commonest way a correctly indexed table still scans, which no amount of adding indexes fixes. Without it, a learner reading a plan that shows a sequential scan on an indexed column has no explanation available and will conclude the planner is broken. Its Apply question — classify predicates as index-usable or not, and rewrite the ones that are not — is distinct from every other node here.