DECLARE
    v_clob  CLOB;
    v_clb2  CLOB;
    v_vch2  VARCHAR2(4000);
    v_vch3  VARCHAR2(4000);
BEGIN

    v_clob := NULL;
    v_vch2 := '1';
    v_clb2 := '1';

    dbms_output.put_line(TO_CHAR(SYSDATE, 'hh24:mi:ss'));

    FOR i IN 1..18000 LOOP
        v_clob := v_clob || v_vch2 || v_vch2 || v_clb2;
    END LOOP; -- 4 сек

    dbms_output.put_line(TO_CHAR(SYSDATE, 'hh24:mi:ss'));

    FOR i IN 1..18000 LOOP
        v_clob := v_clob || (v_vch2 || v_vch2 || v_clb2);
    END LOOP; -- менее 1 сек

    dbms_output.put_line(TO_CHAR(SYSDATE, 'hh24:mi:ss'));


END;

create table t as select 1 a, 2 b from dual
create table t1 as select 3 c, 4 d from dual

with t as (select t1.*, -2 y from hr.t1)
select *
  from (with t1
             as (select t0.*, -1 x
                   from hr.t t0)
        select *
          from t1),
       t,
       t1;

with z as (select * from dual)
select *        
from non_existent_schema.z

select test_user, sum(case when test_param = 'Y' then 1 else 0 end)
  from test_table
 where 1=1
 group by test_user

select test_user, sum(case when test_param = 'Y' then 1 else 0 end)
  from test_table
 where 1=1
 group by test_user

select test_user, count(*)
  from test_table
 where test_param = 'Y'
 group by test_user

select test_user, count (*)
  from test_table
 where test_param = 'Y'
 group by test_user;

       initcap(substr(sname,1,instr(sname,' ')-1)) "Фамилия",
       initcap(substr(sname,instr(sname,' ')+1,instr(sname,' ',instr(sname,' ',instr(sname,' ')+1))-1-instr(sname,' '))) "Имя",
       initcap(substr(sname,instr(sname,' ',instr(sname,' ',instr(sname,' ')+1))+1,length(sname))) "Отчество",