Explaining a Script | Dataford Interview Questions

Your question is Explaining a Script. Take a moment with it on the right.

Talk me through your thinking if you like. When you're confident, submit your answer and I'll grade it like a real screen (7/10 or better passes).

Problem

NIUM's support team pulls up this query whenever a customer calls in asking why their cross-border transfer report looks off. It's meant to summarize, per customer, how many transfers they've sent in each currency and the total value in USD.

-- transfers(id, customer_id, status, amount, currency, fx_rate, created_at)
-- fx_rates(currency, rate_date, rate)
-- customers(id, name, country)

SELECT
    c.name,
    c.country,
    t.currency,
    COUNT(t.id) AS transfer_count,
    SUM(t.amount * f.rate) AS total_usd
FROM transfers t, customers c
LEFT JOIN fx_rates f ON f.currency = t.currency
WHERE t.customer_id = c.id
   OR t.status = 'failed'
  AND t.created_at > '2026-01-01'
GROUP BY c.name, c.country, t.currency;

Describe exactly what this query returns today, including anything about its logic that would surprise a support agent who assumed it's simply "transfer counts and totals per customer."

Your question is Explaining a Script. Take a moment with it on the right.

Talk me through your thinking if you like. When you're confident, submit your answer and I'll grade it like a real screen (7/10 or better passes).

-- transfers(id, customer_id, status, amount, currency, fx_rate, created_at)
-- fx_rates(currency, rate_date, rate)
-- customers(id, name, country)

SELECT
    c.name,
    c.country,
    t.currency,
    COUNT(t.id) AS transfer_count,
    SUM(t.amount * f.rate) AS total_usd
FROM transfers t, customers c
LEFT JOIN fx_rates f ON f.currency = t.currency
WHERE t.customer_id = c.id
   OR t.status = 'failed'
  AND t.created_at > '2026-01-01'
GROUP BY c.name, c.country, t.currency;

Describe exactly what this query returns today, including anything about its logic that would surprise a support agent who assumed it's simply "transfer counts and totals per customer."