select 
  IsNull(b.b_id, s.s_id) AS t_id, 
  IF s.s_id IS NULL THEN b.b_value ELSE s.s_value ENDIF AS t_value
from 
  big_table b 
    full outer join small_table s on (b.b_id=s.s_id)
order by  1 ,  2 ;

SELECT *
FROM sa_table_page_usage ( )
WHERE TableName = 'big_table'

truncate table big_table;
truncate table small_table;

begin
	declare @big_size int;
	declare @small_size int;
	declare @i int;
	
	//Тестовые данные
	set @big_size= 100000 ;
	set @small_size= 1000 ;
	set @i= 1 ;
	while @i<=@big_size loop
		insert into big_table( b_id, b_value )
			values (@i, @i);
		set @i=@i+ 1 ;
	end loop;
	set @i= 1 ;
	while @i<=@small_size loop
		insert into small_table( s_id, s_value)
			values (@i* 2 ,  0 );
		set @i=@i+ 1 ;
	end loop;
end;

commit;

SELECT Count(*)
FROM big_table;

SELECT Count(*)
FROM small_table;

CREATE INDEX "b_id" ON "DBA"."big_table" ( "b_id" ASC ) IN "SYSTEM";

SELECT s.s_id, s.s_value
FROM small_table s
  LEFT JOIN big_table b ON b.b_id = s.s_id
UNION ALL
SELECT b_id, b_value
FROM big_table
WHERE b_id NOT IN (
      SELECT s_id
      FROM small_table )
ORDER BY  1 ,  2 

SELECT s.s_id, s.s_value
FROM small_table s
UNION ALL
SELECT b_id, b_value
FROM big_table
WHERE b_id NOT IN (
      SELECT s_id
      FROM small_table )
ORDER BY  1 ,  2 [/quot]