Keep searched columns free of functions and expressions in predicates
perf-015
Intent
Functions, arithmetic, and other expressions on searched columns can disable normal index usage and turn targeted lookups into scans.
Applicability
Applies when the diff adds or changes SQL or ORM predicates over persisted relational data in WHERE or join conditions. Return unknown if the diff contains no relational predicates or the storage layer is not visible enough to judge index usage.
What to inspect
Changed SQL predicates, ORM filter expressions, join conditions, and any related schema changes such as expression indexes, normalized columns, or case-insensitive collations.
Pass criteria
The predicate compares the raw searched column to a parameter, literal, or range bound, or the repository shows an intentional matching expression index or normalized search column for that predicate.
Fail criteria
The diff wraps a searched column in a function, cast, arithmetic expression, concatenation, or similar transformation that obscures the indexable value being searched.
Do not flag
Do not flag predicates backed by an explicit matching expression or function-based index added or already present in the repository. Do not flag databases or columns that are explicitly configured for case-insensitive comparison so that no column-side function is needed. Do not flag test fixtures or throwaway maintenance scripts that are clearly not production query paths.
Confidence guidance
HIGH when the changed predicate directly applies a function or expression to the searched column and no compensating index is visible. MEDIUM when the query shape is clear, but the presence of an existing expression index is only partially visible. LOW when the predicate is visible, but repository evidence about the underlying schema is weak.
Remediation
Move the transformation to the parameter side or add a normalized column or matching expression index for the intended search.
Pass example
SELECT id
FROM users
WHERE created_at >= :cutoff;
Fail example
SELECT id
FROM users
WHERE DATE(created_at) = :day;