DO $$ 
DECLARE 
 v_id bigint; 
begin 
 --1.
 INSERT INTO r_test_a (name, value, unit, mode, uid, create_ts) 
 SELECT 't_t','','',2,0, extract(epoch from now())::bigint 
 WHERE NOT EXISTS (SELECT id FROM r_test_a WHERE name = 't_t' AND value = '' AND unit = '' AND uid =0);
 --2.
 SELECT id into v_id from r_test_a WHERE name = 't_t' AND value = '' AND unit = '' AND uid = 0;
 --3.
 DELETE FROM r_test_b a WHERE a.obj_id = 'xxx' AND a.file_id = 'ooo' AND a.id IN (SELECT id FROM r_test_a b WHERE b.name = 't_t' AND b.uid=0); 
 --4.
 INSERT INTO r_test_b (id, obj_id, file_id, create_ts) SELECT v_id,'xxx','ooo', extract(epoch from now())::bigint ;
end 
$$;

[ <<label ]
[ DECLARE
 declarations ]
BEGIN
 statements;
 ...
END [ label ];

DO $$
<<first_block
DECLARE
 counter integer := 0;
BEGIN
 counter := counter + 1;
 RAISE NOTICE 'The current value of counter is %', counter;
END first_block $$;

NOTICE: The current value of counter is 1 

DO
'<<first_block
DECLARE
 counter integer := 0;
BEGIN 
 
 counter := counter + 1;
 RAISE NOTICE ''The current value of counter is %'', counter;
 
END first_block';

DO $$ 
<<outer_block
DECLARE
 counter integer := 0;
BEGIN 
 counter := counter + 1;
 RAISE NOTICE 'The current value of counter is %', counter;
 
 DECLARE 
  counter integer := 0;
 BEGIN 
  counter := counter + 10;
  RAISE NOTICE 'The current value of counter in the subblock is %', counter;
  RAISE NOTICE 'The current value of counter in the outer block is %', outer_block.counter;
 END;
 
 RAISE NOTICE 'The current value of counter in the outer block is %', counter;

NOTICE: The current value of counter is 1
NOTICE: The current value of counter in the subblock is 10
NOTICE: The current value of counter in the outer block is 1
NOTICE: The current value of counter in the outer block is 1