Hello, you will realize that only the first row in your table has no value for the previous_transId. But then it is easy to not only show this in the table but also use it to select between the different formulas. If there is a previous then use the formula using it and **else** use the formula for the first record. I think the **case** will be your future helper!
~~~
SELECT *,
(GrowthPool-GCOVAW)/1000000-EstGrowth as Diff
FROM (
SELECT
TransactionId,
GrowthPool,
TransactionId as current_transId,
lag(TransactionId,1) OVER w as previous_transId,
case when lag(TransactionId,1) OVER w
then ((TransactionId) - (lag(TransactionId,1,1) OVER w))*0.003*250
else TransactionId *0.003*250
end as EstGrowth,
lag(GrowthCarry) OVER
w Previous_GCOV, GrowthCarry as Current_GCOV,
(lag(GrowthCarry) OVER w) as GCOVAW
FROM CalculateGrowth
WINDOW w AS (PARTITION BY PIG ORDER BY PIG)
) e
WHERE EstGrowth IS NOT NULL;
~~~