test=# create table tab_a as select (random()*10000000)::int as id, repeat(md5(s::text), 20) as value from generate_series(1, 5000000) s;
SELECT 5000000
test=*# create table tab_b as select (random()*10000000)::int as id, repeat(md5(s::text), 20) as value from generate_series(1, 50000) s;
SELECT 50000