sql - Postgres Update column with another rows data -

ok have 2 tables

measures attr_id, period, net_orders, ref_1 (key = attr_id,period) 

and

policy attr_id, lead_time  

what need grab 'net_orders' measure @ period (which date), add 'lead_time' , update measure table 'ref_1' period = period+lead

i have select gets me data need keep losing myself in head when trying figure out clauses.

select    m.attr_id,    m.period,    m.net_orders,    p.lead_time,   date(m.period) + cast(p.lead_time integer) updateperiod    measures m    inner join policy p on p.attr_id = m.attr_id 

i stuck of following query - aka incomplete

update   measures m set   ref_1 = (select m1.net_orders measures m1             m1.attr_id = m.attr_id , m1.period = m.period)   attr_id = (select m3.attr_id               measures m3 m3.attr_id = m.attr_id                 , m3.period = m.period)   , m.period = (select date(m2.period) + cast(p2.lead_time integer)               measures m2 inner join policy p2 on p2.attr_id = m2.attr_id              m2.attr_id = m.attr_id , m2.period = m.period) 

edit

update measures m set reference_1 = s.net_orders (     select         m.attribute_id, period, net_orders,         date(period) + cast(lead_time integer) periodlevel             measures m         inner join policies p on p.attribute_id = m.attribute_id ) s     m.attribute_id = s.attribute_id     , m.period = s.periodlevel 

this query has ended working. getting errors first answer looks working now!

update measures m set ref_1 = s.net_orders (     select         m.attr_id, period, net_orders,         period::date + lead_time::int period             measures m         inner join         policy using(attr_id) ) s     s.attr_id = m.attr_id     , s.period = m.period::date