Wanted to knowwhere my query exactly going wrong as I am not having piaggregate table in PI DA

Hi All, I am having piavg,pistd,picoutn as 3 different table and I wanted to have data for a tag from all these 3 tables within a timestamp of 10 mins.When I try to do with join then I am getting a count of 3600 but when I try to run individual query of count then I am getting 600 for timespan of 10 min . Can anyone please explain where I am getting wrong or what exactly is wrong in this case :

SELECT 

  a.tag,

  a.time,

  a.value AS AvgValue,

  s.value AS StdDevValue,

  c.value AS SampleCount

FROM 

  piarchive..piavg a

JOIN 

  piarchive..pistd s ON a.tag = s.tag AND a.time = s.time

JOIN 

  piarchive..picount c ON a.tag = c.tag AND a.time = c.time

WHERE 

  a.tag IN ('tagname1') AND

  a.time BETWEEN '*-10m' AND '*' AND

  a.timestep = '10m'

ORDER BY 

  a.time;