FIRST_VALUE

1
SELECT
2
  customer_id,
3
  order_date,
4
  amount,
5
  FIRST_VALUE(order_date) OVER (
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    PARTITION BY customer_id
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    ORDER BY order_date
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  ) as first_order
9
FROM orders;

1
SELECT
2
  date,
3
  stock_price,
4
  stock_price - FIRST_VALUE(stock_price) OVER (ORDER BY date) as change_from_start
5
FROM stock_prices;