FA-159 / Storage and queries / Member archive

String-encoded composite keys merge unrelated groups · case 04

Distinct two-column groups collapse together because their concatenated or delimiter-separated key strings coincide.

Member previewVariant 4 · 3 implementations · 7 checks per implementation

Case contract

Rows contain [first_string,second_string,integer_amount]. Group by exact ordered pairs and return sorted [first,second,total] rows. Components may be empty or contain delimiter characters; input occurrences are all counted.

Why this case matters

Models compound keys in aggregation caches and client-side query engines. The fixtures expose both simple concatenation collisions and delimiter collisions without relying on hash collisions or randomized behavior.

One recorded failure

Sample boundary fixture

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

Boundary fixture	Actual	Expected	Outcome
unseparated component boundaries collide	`[["ab", "c", 9]]`	`[["a", "bc", 5], ["ab", "c", 4]]`	Failed

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