Oracle 18c

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create table tab1 (id int, doc clob)
create table tab2 (id int, doc clob)
create or replace procedure proc (id int) is
begin
    insert into tab2 values (id, (select doc from tab1 where id = proc.id)); 
    dbms_output.put_line (sql%rowcount||' row into tab2 inserted.'); 
end;
/
create or replace trigger tr_example
after insert on TAB1 for each row
begin 
    proc (:new.id);
end;
/
insert into tab1 values (1, 'document')
ORA-04091: table FIDDLE_PAQMTIXUZRHSTARLXOYK.TAB1 is mutating, trigger/function may not see it
ORA-06512: at "FIDDLE_PAQMTIXUZRHSTARLXOYK.PROC", line 3
ORA-06512: at "FIDDLE_PAQMTIXUZRHSTARLXOYK.TR_EXAMPLE", line 2
ORA-04088: error during execution of trigger 'FIDDLE_PAQMTIXUZRHSTARLXOYK.TR_EXAMPLE'