DBMS_SCHEDULER作业“cleanup_job”如下所示。

DECLARE
  stmt VARCHAR2(4000) := '
    BEGIN
      DELETE FROM useraccounts WHERE accountcreatedate < trunc(sysdate) - 90;
      DELETE FROM usertasks WHERE userid NOT IN (SELECT userid FROM useraccounts u where u.userid=userid);
                    
      BEGIN
        EXECUTE IMMEDIATE ''ALTER TABLE usertasks ADD CONSTRAINT FK_Useraccounts FOREIGN KEY (userid) REFERENCES useraccounts(userid) ON DELETE CASCADE'';
      EXCEPTION WHEN OTHERS THEN
        IF SQLCODE = -02275 THEN
          /*ORA-02275: such a referential constraint already exist*/
          DBMS_OUTPUT.PUT_LINE(''Foreign Key : FK_Useraccounts on Delete Cascade in table usertasks already exists'');
        ELSE
          RAISE;
        END IF;
      END
    END;';
BEGIN
  DBMS_SCHEDULER.CREATE_JOB (
    job_name   => 'cleanup_job',
    job_type   => 'PLSQL_BLOCK',
    job_action => stmt,
    start_date => sysdate, 
    auto_drop  => true, 
    comments   => 'Job to cleanup user accounts whose creation date > 90 days',
    enabled    => TRUE
  );
EXCEPTION
  WHEN OTHERS THEN
    IF SQLCODE = -27477 THEN
      DBMS_OUTPUT.PUT_LINE('Skipped job creation - a cleanup_job already exists for this service.');
    ELSE
      RAISE;
    END IF;
END;

如果我在单个PLSQLBlock中给予所有SQL语句，

stmt varchar(4000) ='
  BEGIN
    ---All SQL Statements here----
  END;'

但是，如果我有嵌套PL SQL块，则在运行作业时没有错误，但语句没有执行（在关联的表中看不到任何更改）。

stmt varchar(4000) ='
   BEGIN
     ---SQL Statements----
      BEGIN
         ----SQL Statements-----
      END;
    END;'

是否不允许将嵌套PL/SQL块分配给变量？
我对这个很陌生，任何帮助都将不胜感激。