FA-44825 / Data systems / Member archive

Scalar subquery cardinality counts distinct values · case 05

Scalar subquery cardinality counts distinct values.

Member previewVariant 5 · 3 implementations · 9 checks per implementation

Case contract

Evaluate a correlated scalar lookup per outer key. Zero rows yield None, exactly one row yields its value including None, and two or more matching rows yield the explicit value CARDINALITY. Count physical rows, not distinct or non-null values.

Why this case matters

A bounded deterministic data engine model makes representation and changelog faults reproducible.

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
duplicate physical rows	`[5]`	`["CARDINALITY"]`	Failed

MEMBER ARCHIVE

The complete case is available to members.

This record includes three runnable implementations, regression fixtures, execution results, and source hashes.

Member access is invitation-based. Sign in with your invited account to inspect the sources.