Why might the order of elements in the array returned by ARRAY_AGG differ between query executions if no ORDER BY is specified inside it?

hard📝 Conceptual Q10 of 15

PostgreSQL - Aggregate Functions and GROUP BY

Why might the order of elements in the array returned by ARRAY_AGG differ between query executions if no ORDER BY is specified inside it?

ABecause ARRAY_AGG always sorts elements alphabetically by default

BBecause SQL tables represent unordered sets, so aggregation order is not guaranteed

CBecause ARRAY_AGG caches results and returns them in fixed order

DBecause GROUP BY forces sorting of aggregated arrays

Step-by-Step Solution

Solution:

Step 1: Understand SQL table ordering
Tables represent unordered sets; row order is not guaranteed without ORDER BY.
Step 2: Effect on ARRAY_AGG
Without ORDER BY inside ARRAY_AGG, element order depends on query plan and can vary.
Final Answer:
Because SQL tables represent unordered sets, so aggregation order is not guaranteed -> Option B
Quick Check:
ARRAY_AGG order is undefined without ORDER BY [OK]

Quick Trick: Always use ORDER BY inside ARRAY_AGG for consistent element order [OK]

Common Mistakes:

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