could anyone suggestion me as below coding condition matching or not? if diff value = 0

if NOT EXISTS (Select A.MACHINE, A.Instance, B.InstanceA,

(B.InstanceA-A.Instance) as Diff from (select MACHINE, COUNT(*)

as Instance from PROD.dbo.CM_INSTANCE group by MACHINE) A,

(Select COUNT(*)/4 as InstanceA from PROD.dbo.CM_INSTANCE) B

where (B.InstanceA-A.Instance) < -3 or (B.InstanceA-A.Instance) > 3)

begin

EXEC msdb.dbo.sp_send_dbmail @profile_name='db_mail',

@recipients='ananad.murugesan@ril.com',

@subject='Alert!-Verify LIMS Instance',

@query= 'Select A.MACHINE, A.Instance, B.InstanceA,

(B.InstanceA-A.Instance) as Diff from (select MACHINE, COUNT(*)

as Instance from PROD.dbo.CM_INSTANCE group by MACHINE) A,

(Select COUNT(*)/4 as InstanceA from PROD.dbo.CM_INSTANCE) B

where (B.InstanceA-A.Instance) < -3 or (B.InstanceA-A.Instance) > 3'

end