Using a loop in SQL to populate the table (SQL Server) - sql

Question

I am quite new with SQL and loops especially and need some help with the following problem.
I have a table like this:
SpotID EventID MaxTemp
123 1 45
236 1 109
69 1 18
123 2 216
236 2 29
69 2 84
123 3 91
236 3 457
69 3 280
I would like to generate a new table with the following output:
SpotID Over30 Over70 Over100
123 3 2 1
236 2 2 2
69 2 2 1
So what i am after is the count of how many times did the temperature exceed the limits of 30, 70 and 100 per SpotID for different EventIDs.
Is there a way to do this with a loop? My data set is obviously bigger and I am curious if how could i use something efficient.
Thank you very much.
Mike

Answer 1

You just need conditional aggregation:
select spotid,
sum(case when maxtemp > 30 then 1 else 0 end) as over_30,
sum(case when maxtemp > 70 then 1 else 0 end) as over_70
sum(case when maxtemp > 100 then 1 else 0 end) as over_100
from likethis
group by spotid;

Answer 2

If you just want to learn how to use loops....
DECLARE #DATA TABLE (
SpotID INT,
EventID INT,
MaxTemp INT
);
DECLARE #NEWDATA TABLE (
SpotID INT,
T30 INT,
T90 INT,
T100 INT
);
DECLARE
#SPOT AS INT,
#T30 AS INT,
#T90 AS INT,
#T100 AS INT;
INSERT INTO #DATA VALUES
(123, 1, 45 ),
(236, 1, 109),
(69 , 1, 18 ),
(123, 2, 216),
(236, 2, 29 ),
(69 , 2, 84 ),
(123, 3, 91 ),
(236, 3, 457),
(69 , 3, 280);
DECLARE STATION CURSOR FOR SELECT SpotID FROM #DATA GROUP BY SpotID;
OPEN STATION;
FETCH NEXT FROM STATION INTO #SPOT;
WHILE ##FETCH_STATUS = 0
BEGIN
SET #T30 = 0;
SET #T90 = 0;
SET #T100 = 0;
SELECT
#T30 = SUM(CASE WHEN MaxTemp > 30 AND MaxTemp < 70 THEN 1 ELSE 0 END),
#T90 = SUM(CASE WHEN MaxTemp >= 70 AND MaxTemp < 100 THEN 1 ELSE 0 END),
#T100 = SUM(CASE WHEN MaxTemp >= 100 THEN 1 ELSE 0 END)
FROM #DATA WHERE SpotID = #SPOT
INSERT INTO #NEWDATA VALUES (#SPOT,#T30,#T90,#T100)
FETCH NEXT FROM STATION INTO #SPOT;
END;
CLOSE STATION;
DEALLOCATE STATION;
SELECT * FROM #NEWDATA
Not anyway I would write the code requested, but this example shows how to create table variables, a simple cursor for looping, and writing to answers to variables that are loaded into a new table.
A lot of moving parts but it can give you insight to doing loops.

Answer 3

One minor change to the previous post, my version only counts within each temp range, else the lower temps will count most temps not temps in that range.
DECLARE #DATA TABLE (
SpotID INT,
EventID INT,
MaxTemp INT
)
INSERT INTO #DATA VALUES
(123, 1, 45 ),
(236, 1, 109),
(69 , 1, 18 ),
(123, 2, 216),
(236, 2, 29 ),
(69 , 2, 84 ),
(123, 3, 91 ),
(236, 3, 457),
(69 , 3, 280)
SELECT
SpotID,
SUM(CASE WHEN MaxTemp > 30 AND MaxTemp < 70 THEN 1 ELSE 0 END) AS OVER_30,
SUM(CASE WHEN MaxTemp >= 70 AND MaxTemp < 100 THEN 1 ELSE 0 END) AS OVER_70,
SUM(CASE WHEN MaxTemp >= 100 THEN 1 ELSE 0 END) AS OVER_100
FROM
#DATA
GROUP BY
SpotID