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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.

Questions this Concept answers

  • Why does a pattern match with a leading wildcard defeat an index on the column?