Database:  192.168.0.220/3253:/var/db/fb25/production25.fdb
SQL> create sequence g;
SQL> recreate table t1(id int primary key using index t1_pk, x int);
SQL> recreate table t2(id int primary key using index t2_pk, x int);
SQL> commit;
SQL>
SQL> insert into t1 select gen_id(g,1), rand()*100 from rdb$types rows 10;
SQL> commit;
SQL>
SQL> alter sequence g restart with 0;
SQL> commit;
SQL>
SQL> insert into t2 select gen_id(g,1), rand()*100 from rdb$types rows 50;
SQL> commit;
SQL>
SQL> set term ^;
SQL> execute block returns(processed_rows int) as
CON> begin
CON>   merge into t1 t using t2 s on t.id=s.id
CON>   when MATCHED then update set t.x=t.x+s.x
CON>   when NOT matched then insert values(s.id, s.x);
CON>   processed_rows = row_count;
CON>   suspend;
CON> end
CON> ^set term ;^

PROCESSED_ROWS
==============
             1

SQL> rollback;