You have a table transactions with columns user_id and amount. How do you find the total amount spent by each user?

hard📝 Application Q8 of 15

PostgreSQL - Aggregate Functions and GROUP BY

You have a table transactions with columns user_id and amount. How do you find the total amount spent by each user?

ASELECT user_id, COUNT(amount) FROM transactions GROUP BY amount;

BSELECT SUM(amount) FROM transactions WHERE user_id;

CSELECT user_id, SUM(amount) FROM transactions GROUP BY user_id;

DSELECT user_id, AVG(amount) FROM transactions;

Step-by-Step Solution

Solution:

Step 1: Use SUM to total amounts per user
SUM(amount) adds amounts for each user.
Step 2: Group results by user_id
GROUP BY user_id groups transactions by each user.
Final Answer:
SELECT user_id, SUM(amount) FROM transactions GROUP BY user_id; -> Option C
Quick Check:
SUM with GROUP BY user_id totals per user [OK]

Quick Trick: Use GROUP BY with SUM to total per group [OK]

Common Mistakes:

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