using rank() and window functions in Greenplum

Define and name a window specification. Reuse window specification throughout the query

sachi=# select region,rank() over (order by year) from sachi.sales;

 region | rank 

--------+------

 asia   |    1

 usa    |    2

(2 rows)

                                                            ^

sachi=# select region, rank() over (W) from sachi.sales WINDOW W as (order by year);

 region | rank 

--------+------

 asia   |    1

 usa    |    2

(2 rows)