Running Total in Transactions | Dataford Interview Questions

How would you calculate running total in a transaction table

Asked in the Round 1 stage and asked to write SQL code. A reported follow-up was: How do you handle deposits and withdrawals in running total logic with syntax.

Output

Return one row per transaction with account_id, transaction_id, occurred_at, transaction_type, amount, signed_amount, and running_total.
Deposits increase the total, withdrawals decrease it, and NULL amounts contribute zero.
Order by account_id, occurred_at, and transaction_id.

Schema

transactions

Column	Type	Description
transaction_idPK	INT	Unique transaction identifier
account_id	INT	Account associated with the transaction
occurred_at	TIMESTAMP	Timestamp when the transaction occurred
transaction_type	VARCHAR(20)	Transaction direction, either deposit or withdrawal
amount	DECIMAL(12,2)	Transaction amount
currency	VARCHAR(3)	ISO currency code

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