Question

I have a temperature table, which contains a DATETIME field and a temperature field which is type of float. There are temperature measurements taken every 30 minutes so it’s 48 times a day. What I want to do is to select a date range (eg. 2012-01-01 to 2012-05-01), calculate each day’s average temperature and return the average temperature of each day in the range. Solutions?

Thanks

Answer 1

Use DATE() to strip off the time portion of the datetime field, and use it in the GROUP BY clause for the aggregate AVG() of the temperature column. Your WHERE clause will filter the date range you want to find.

SELECT
  DATE(temp_date) AS theday,
  AVG(temperature) AS avgtmp
FROM
  temp_readings
WHERE DATE(temp_date) BETWEEN '2012-01-01' AND '2012-05-01'
GROUP BY theday

Note: From your description, it sounds like every day does have readings, but if any day does not appear in your readings table, it will be absent from your result set here.