SQL rewrite - Group by - response (1) by dnoeth

First i would simplify the calculation on LOG_TIME, why do you cast every part to a string? 

CAST((log_time (FORMAT 'hh:mi:ss')) AS CHAR(8)) AS HOUR_MIN_SEC

You might also avoid typecasting to a string: 

log_time - ((EXTRACT(SECOND FROM log_time) MOD 1) * INTERVAL '1' SECOND)

Based on your query i'm not shure if you want the count per minute, then simply remove the "mod 1" (or change the FORMAT).
And then it's just a QUALIFY:

SELECT 
   LOG_DATE,
   log_time - ((EXTRACT(SECOND FROM log_time) MOD 1) * INTERVAL '1' SECOND) AS HOUR_MIN_SEC,
   COUNT(*) AS Downloads_Per_Second
FROM CDN_RQST_EVT
WHERE LLNW_REDRCT_STAT_CODE IN ('DVR%20STATUS%3A%20DOWNLOAD_COMPL',' DOWNLOAD_COMPLETED')
AND LOG_DATE BETWEEN '2013-03-11'  AND '2013-03-17' 
--AND LOG_TIME < '09:00:00'
GROUP BY 1,2
QUALIFY 
   ROW_NUMBER() 
   OVER (PARTITION BY Log_Date, EXTRACT(HOUR FROM HOUR_MIN_SEC) 
         ORDER BY Downloads_Per_Second DESC) = 1

 
Dieter