0 - 3 of 3 tags for cpu time

Hi all. We're working on creating operational reports to measure key metrics for Teradata 13.10. We typically use DBQL/Acctg to report on users and ResUsage tables for platform-wide metrics.
 

I have written a query as follows :
select
a.x1,
a.x2,
b.x3
from
(select x1,x2,x4 from table1 where 'some conditions') as a
inner join
(select x3,x4 from table2) as b
on
a.x3=b.x3
 
I have another version as :
select
a.x1,
a.x2,
b.x3
from

when select inserting from one table to another -- where both have compression on the same column...  what does teradata do?  Does it need to decompress each & every column first -- to get the value and then attempt to insert it into the destination table by check each compressed value there & then storing it?