Selecting first and last values in a group

Question

I have a MySql table consisting of daily stock quotes (open, high, low, close and volume) which I\'m trying to convert into weekly data on the fly. So far, I have the follow

Answer 1

Starting with MySQL 8, you would ideally use window functions for the task:

WITH 
  t1 AS (
    SELECT _low, _high, _volume, CONCAT(YEAR(_date), "-", WEEK(_date)) AS myweek
    FROM mystockdata
  ),
  t2 AS (
    SELECT 
      t1.*, 
      FIRST_VALUE(_open) OVER (PARTITION BY myweek ORDER BY _date) AS first_open,
      FIRST_VALUE(_close) OVER (PARTITION BY myweek ORDER BY _date DESC) AS last_close
    FROM t1
  )
SELECT MIN(_low), MAX(_high), AVG(_volume), myweek, MIN(first_open), MAX(last_close)
FROM t2
GROUP BY myweek
ORDER BY myweek;