ORA-30926 unable to get a stable set of rows in the source tables

select * from tb_test;

insert into tb_test(CODE, TEXT) values (1, 'test');

-- 这里正常

merge into tb_test t

using (select 1 code,'test' text from dual union all

       select 1 code,'test' text from dual) s

on (t.code = s.code)

when matched then

update set t.text = s.text;

-- 这里 error: ORA-30926

merge into tb_test t

using (select 1 code,'test1' text from dual union all

       select 1 code,'test1' text from dual) s

on (t.code = s.code)

when matched then

update set t.text = s.text;

-- 这里 error: ORA-30926

merge into tb_test t

using (select 1 code,'test1' text from dual union all

       select 1 code,'test2' text from dual) s

on (t.code = s.code)

when matched then

update set t.text = s.text;