SQL Server Percent Difference is Greater than Value - sql

Question

I have the following table structures:
table c_alert:
|dynamic|symbol|price_usd|
--------------------------
|5 |BTC |13000 |
table c_current:
|symbol|price_usd|
------------------
|BTC |13600 |
I have this query:
SELECT dbo.c_alert.symbol, dbo.c_alert.price_usd AS alert_price, dbo.c_current.price_usd AS current_price, (dbo.c_current.price_usd - dbo.c_alert.price_usd) * 100.0 / dbo.c_alert.price_usd AS pct_diff, dbo.c_alert.dynamic AS pct
FROM dbo.c_alert INNER JOIN
dbo.c_current
ON dbo.c_alert.symbol = dbo.c_current.symbol AND
dbo.c_alert.dynamic > (dbo.c_current.price_usd - dbo.c_alert.price_usd) * 100.0 / dbo.c_alert.price_usd
Which returns this:
|symbol|alert_price|current_price|pct_diff|dynamic|
-----------------------------------------------
|BTC |13000 |13613.3000 |4.7 |5 |
Not very strong with financial queries...Basically I would like to know when the price difference between alert_price and current_price are equal to or greater than value in the dynamic column as a boolean. So where the difference is equal or greater than 5% show True, else False. That dynamic value (integer) could change for each row in the c_alert table. Hope someone can provide a solution to the query.

Answer 1

Because the same percent difference term is required in multiple places in the query, I might go with using a CTE first, which calculates this term. Then, do a straightforward query on the CTE to get the output you want.
WITH cte AS (
SELECT
t2.symbol,
t2.dynamic,
t2.price_usd AS alert_price,
t1.price_usd AS current_price,
100.0*(t1.price_usd - COALESCE(t2.price_usd, 0.0)) / t2.price_usd AS pct_diff
FROM dbo.c_current t1
LEFT JOIN dbo.c_alert t2
ON t1.symbol = t2.symbol
)
SELECT
symbol,
alert_price,
current_price,
pct_diff,
dynamic,
CASE WHEN pct_diff > dynamic THEN 'TRUE' ELSE 'FALSE' END AS result
FROM cte;
Edit:
The logic seems to be working in the demo below. If you still have issues, then edit the demo and paste the link somewhere as a comment.
Demo

Answer 2

Use table aliases so your query is easier to write and to read. Then just use a case:
SELECT a.symbol, a.price_usd AS alert_price,
c.price_usd AS current_price,
(c.price_usd - a.price_usd) * 100.0 / a.price_usd AS pct_diff,
a.dynamic AS pct,
(case when (a.price_usd - c.price_used) > a.dynamic
then 'true' else 'false'
end) as flag
FROM dbo.c_alert a INNER JOIN
dbo.c_current c
ON a.symbol = c.symbol AND
a.dynamic > (c.price_usd - a.price_usd) * 100.0 / a.price_usd;
SQL Server doesn't have a boolean type, so this uses a string. You can use 0 and 1 instead.