[Solved] What is wrong with this query?SELECT customer_id, COUNT(*) FROM orders; — Ans: Missing GROUP BY clause for customer_id | PostgreSQL

PostgreSQL - Aggregate Functions and GROUP BY

What is wrong with this query?

SELECT customer_id, COUNT(*) FROM orders;

Acustomer_id must be inside COUNT()

BCOUNT(*) cannot be used without WHERE

CMissing GROUP BY clause for customer_id

DSELECT must have ORDER BY with COUNT

Step-by-Step Solution

Solution:

Step 1: Check aggregation with non-aggregated column
customer_id is selected but not aggregated or grouped.
Step 2: Identify missing GROUP BY
To use COUNT(*) with customer_id, GROUP BY customer_id is required.
Final Answer:
Missing GROUP BY clause for customer_id -> Option C
Quick Check:
Non-aggregated columns need GROUP BY [OK]

Quick Trick: Use GROUP BY when mixing columns with aggregation [OK]

Common Mistakes:

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What is wrong with this query?