[Solved] Find the issue in this query:SELECT ARRAY_AGG(DISTINCT product) FROM orders GROUP BY customer_id; — Ans: Missing customer_id in SELECT list when using GROUP BY | PostgreSQL

PostgreSQL - Aggregate Functions and GROUP BY

Find the issue in this query:

SELECT ARRAY_AGG(DISTINCT product) FROM orders GROUP BY customer_id;

AMissing customer_id in SELECT list when using GROUP BY

BARRAY_AGG does not support DISTINCT keyword

CCannot use DISTINCT inside ARRAY_AGG with GROUP BY

DGROUP BY should be removed for ARRAY_AGG

Step-by-Step Solution

Solution:

Step 1: Understand GROUP BY requirements
When grouping by customer_id, it must appear in SELECT list to identify groups.
Step 2: Check ARRAY_AGG with DISTINCT
ARRAY_AGG supports DISTINCT; no error there.
Final Answer:
Missing customer_id in SELECT list when using GROUP BY -> Option A
Quick Check:
GROUP BY columns must be in SELECT list [OK]

Quick Trick: Include GROUP BY columns in SELECT list with ARRAY_AGG [OK]

Common Mistakes:

Master "Aggregate Functions and GROUP BY" in PostgreSQL

9 interactive learning modes - each teaches the same concept differently

Find the issue in this query: