A simple Bar Chart - Daily power consumption

Hi.

I created a daily power consumption bar chart, but it will show only max values.

SELECT
$__timeGroupAlias(lastdate,1d,0),
sum(value) AS ‘Kwh’
FROM mcsmqtt
WHERE
Device = ‘1st_Energy_144-3EM-Energy SUM Hourly’
AND $__timeFilter(lastdate)
GROUP BY lastdate
ORDER BY 1

If I use max(value) - min(value) AS ‘Kwh’ I get all zeros.

SELECT
$__timeGroupAlias(lastdate,1d,0),
max(value) - min(value) AS ‘Kwh’
FROM mcsmqtt
WHERE
Device = ‘1st_Energy_144-3EM-Energy SUM Hourly’
AND $__timeFilter(lastdate)
GROUP BY lastdate
ORDER BY 1

¸

What am I missing here?

Thank you