How to write a SQL query to get sum of transactions?

Question

I want sql query for this. I have three tables customer,account, transaction the schema of the are as below

I want to get customer details, account id, sum of transaction id

Answer 1

You can Sum the transactions grouped by CustomerID and then join to the customers table on the CustomerID like this:

SELECT c.Customer_name, c.Customer_mobile, t.Transaction_sum
FROM Customer c
JOIN (
    SELECT t.CustomerID, SUM(t.Sum) as Transaction_sum
    FROM transactions t
    GROUP BY t.CustomerID
    ) t on t.CustomerID = c.CustomerID

Answer 2

Your query is quite close. Try this:

SELECT c.customer_id, a.Account_id, SUM(t.transaction_amount) as amount
FROM Account a INNER JOIN
     Customer c
     ON a.customer_id = c.customer_id INNER JOIN
     Transaction t
     ON a.account_id = t.account_id
GROUP BY c.customer_id, a.account_id;

Note the use of table aliases to simplify the query. And -- more importantly -- the SELECT columns and GROUP BY columns are consistent.

Because the customer_id is in the Account table, you don't need the Customer table. So, you can simplify this to:

SELECT a.customer_id, a.Account_id, SUM(t.transaction_amount) as amount
FROM Account a INNER JOIN
     Transaction t
     ON a.account_id = t.account_id
GROUP BY a.customer_id, a.account_id;