You have a table Transactions with columns user_id and transaction_value. Which query calculates the average transaction value for each user?
hard📝 Application Q8 of 15
SQL - Aggregate Functions
You have a table Transactions with columns user_id and transaction_value. Which query calculates the average transaction value for each user?
ASELECT user_id, AVG(transaction_value) FROM Transactions GROUP BY user_id;
BSELECT AVG(transaction_value) FROM Transactions WHERE user_id;
CSELECT user_id, SUM(transaction_value)/COUNT(user_id) FROM Transactions;
DSELECT user_id, AVG(transaction_value) FROM Transactions;
Step-by-Step Solution
Solution:
Step 1: Understand grouping
To get average per user, group by user_id is required.
Step 2: Check query syntax
SELECT user_id, AVG(transaction_value) FROM Transactions GROUP BY user_id; uses GROUP BY user_id with AVG(), which is correct.
Step 3: Evaluate other options
SELECT AVG(transaction_value) FROM Transactions WHERE user_id; is invalid syntax; SELECT user_id, SUM(transaction_value)/COUNT(user_id) FROM Transactions; lacks GROUP BY and uses manual average; SELECT user_id, AVG(transaction_value) FROM Transactions; lacks GROUP BY, so returns overall average.
Final Answer:
SELECT user_id, AVG(transaction_value) FROM Transactions GROUP BY user_id; -> Option A
Quick Check:
Use GROUP BY to get averages per group [OK]
Quick Trick:GROUP BY user_id with AVG() calculates per-user average [OK]
Common Mistakes:
MISTAKES
Omitting GROUP BY when aggregating per user
Using invalid WHERE clause for grouping
Calculating average manually without grouping
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