PostgreSQL: how to create both sequence and table simultaneously?
You can create the sequence implicitely through the serial (pseudo) type and then change its current value:

CREATE TABLE mytable (gid serial NOT NULL, size INTEGER); 
select setval('mytable_gid_seq', 100);


or alternatively using

CREATE TABLE mytable (gid serial NOT NULL, size INTEGER); 
alter sequence mytable_gid_seq restart with 100;


This is slightly different than defining a minvalue - but that would only matter if the sequence was set to wrap. This version also creates a link between the sequence and the table, so that the sequence is automatically dropped when the table is dropped (in your script you would need to alter sequence mytable_gid_seq owner to mytable.gid);