Oracle delete data from large tables keeping only a few data (temp table)

gistfile1.txt

--DROP TABLE acctmp3;	  

  DECLARE
    table_name varchar(20);
  begin  
   table_name := 'acctmp';
   DBMS_OUTPUT.PUT_LINE('Deleting table ' ||table_name);
   execute immediate 'truncate table ' || table_name;  
   execute immediate 'drop table ' || table_name;  
    exception  
      when OTHERS then 
          DBMS_OUTPUT.PUT_LINE('Failed to delete table ' || table_name);  
    end; 
  DECLARE
    table_name varchar(20);
  begin  
   table_name := 'acctmp2';
   DBMS_OUTPUT.PUT_LINE('Deleting table ' ||table_name);
   execute immediate 'truncate table ' || table_name;  
   execute immediate 'drop table ' || table_name;  
    exception  
      when OTHERS then 
          DBMS_OUTPUT.PUT_LINE('Failed to delete table ' || table_name);  
    end; 
  DECLARE
    table_name varchar(20);
  begin  
   table_name := 'acctmp3';
   DBMS_OUTPUT.PUT_LINE('Deleting table ' ||table_name);
   execute immediate 'truncate table ' || table_name;  
   execute immediate 'drop table ' || table_name;  
    exception  
      when OTHERS then 
          DBMS_OUTPUT.PUT_LINE('Failed to delete table ' || table_name);  
    end; 

BEGIN TRANSACTION;
  
DECLARE

  keepDays number;
BEGIN
  keepDays := 30;
    
  dbms_output.put_line ('tso_fahrplan_fluss handling') ;
  execute immediate 'LOCK TABLE tso_fahrplan_fluss IN EXCLUSIVE MODE'; 
	execute immediate 'CREATE GLOBAL TEMPORARY TABLE acctmp 
    ON COMMIT PRESERVE ROWS
    AS SELECT * FROM tso_fahrplan_fluss f
    WHERE 1=1 AND exists ( select * 
                            from tso_fahrplan_daten d 
                            where d.tso_fahrplan_fluss_id = f.tso_fahrplan_fluss_id AND cdate>(trunc(sysdate)-' ||  keepDays || '))';
							
      execute immediate 'TRUNCATE table tso_fahrplan_fluss DROP STORAGE';
      execute immediate 'INSERT INTO tso_fahrplan_fluss
        SELECT * FROM acctmp';
      execute immediate 'TRUNCATE TABLE acctmp';
      execute immediate 'DROP TABLE acctmp';
      --SELECT * FROM acctmp;
  
  dbms_output.put_line ('tso_fahrplan_daten handling') ;
  execute immediate 'LOCK TABLE tso_fahrplan_daten IN EXCLUSIVE MODE'; 
	execute immediate 'CREATE GLOBAL TEMPORARY TABLE acctmp2 
    ON COMMIT PRESERVE ROWS
    AS SELECT * FROM tso_fahrplan_daten f
    WHERE 1=1 AND cdate > (trunc(sysdate)-' ||  keepDays || ')';
							
      execute immediate 'TRUNCATE table tso_fahrplan_daten DROP STORAGE';
      execute immediate 'INSERT INTO tso_fahrplan_daten
        SELECT * FROM acctmp2';
      execute immediate 'TRUNCATE TABLE acctmp2';
      execute immediate 'DROP TABLE acctmp2';	  
	  
  dbms_output.put_line ('tso_fahrplan handling') ;
  execute immediate 'LOCK TABLE tso_fahrplan IN EXCLUSIVE MODE'; 
	execute immediate 'CREATE GLOBAL TEMPORARY TABLE acctmp3 
    ON COMMIT PRESERVE ROWS
    AS SELECT * FROM tso_fahrplan f
    WHERE 1=1 AND  f.cdate > (trunc(sysdate)-' ||  keepDays || ')';
							
      execute immediate 'TRUNCATE table tso_fahrplan DROP STORAGE';
      execute immediate 'INSERT INTO tso_fahrplan
        SELECT * FROM acctmp3';
      execute immediate 'TRUNCATE TABLE acctmp3';
      execute immediate 'DROP TABLE acctmp3';	  
END;
COMMIT ;