sql - PostgreSQL MAX() inner query really slow -


i've been tasked optimising of sql queries ran on large datasets. have query below i'm trying optimise @ moment struggling it

the query takes around 40-45 minutes comeback answer not acceptable. take longer dataset grows within db.

i believe inner max() function dramatically slows down query?

i appreciate or advice in making query better , faster.

select    positionview.equipmenttimestamp,    positionview.name,    positionview.inumber,    positionview.datauserprovidername,    positionview.latitude,    positionview.longitude    public.positionview positionview.outbound = false , positionview.referenceidentifier null , positionview.responsetype = 'xyz' , positionview.equipmenttimestamp >='2016-02-02 14:44:08.213' , positionview.equipmenttimestamp <='2016-02-05 14:44:08.213' , positionview.equipmenttimestamp =(   select max(positionview2.equipmenttimestamp)     positionview positionview2     positionview.inumber = positionview2.inumber     , positionview2.outbound = false     , positionview2.referenceidentifier null     , positionview2.responsetype = 'xyz'     , positionview2.equipmenttimestamp >='2016-02-02 14:44:08.213'     , positionview2.equipmenttimestamp <='2016-02-05 14:44:08.213');

many in advance!

this kind of statement can done using postgres' distinct on() operator (which faster equivalent solution using standard window function):

select distinct on (inumber)   equipmenttimestamp,    name,    inumber,    datauserprovidername,    latitude,    longitude    public.positionview outbound = false , referenceidentifier null , responsetype = 'xyz' , equipmenttimestamp >='2016-02-02 14:44:08.213' , equipmenttimestamp <='2016-02-05 14:44:08.213' order inumber, equipmenttimestamp desc;

an index on (inumber,equipmenttimestamp) help


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