[Solved] Given the table products with columns category and name, what is the output of this query?SELECT category, JSON_AGG(name) FROM products GROUP BY category ORDER BY category; | PostgreSQL

PostgreSQL - Aggregate Functions and GROUP BY

Given the table products with columns category and name, what is the output of this query?

SELECT category, JSON_AGG(name) FROM products GROUP BY category ORDER BY category;

A[{"category":"Books","json_agg":["Novel","Comics"]}, {"category":"Toys","json_agg":["Car","Doll"]}]

B[{"category":"Books","json_agg":"Novel,Comics"}, {"category":"Toys","json_agg":"Car,Doll"}]

C[{"category":"Books","json_agg":["Novel"]}, {"category":"Toys","json_agg":["Car"]}]

D[{"category":"Books","json_agg":null}, {"category":"Toys","json_agg":null}]

Step-by-Step Solution

Solution:

Step 1: Understand GROUP BY with JSON_AGG
The query groups rows by category and collects all product names per category into a JSON array.
Step 2: Analyze expected JSON_AGG output
JSON_AGG returns an array of names per category, so each category has a JSON array of product names, not a string or null.
Final Answer:
[{"category":"Books","json_agg":["Novel","Comics"]}, {"category":"Toys","json_agg":["Car","Doll"]}] -> Option A
Quick Check:
JSON_AGG groups names into arrays = [{"category":"Books","json_agg":["Novel","Comics"]}, {"category":"Toys","json_agg":["Car","Doll"]}] [OK]

Quick Trick: JSON_AGG returns arrays, not comma-separated strings [OK]

Common Mistakes:

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Given the table products with columns category and name, what is the output of this query?