truncate table ods_emp drop storage;
 insert into ods_emp select * from emp;

SQL> DECLARE
  v_str VARCHAR();
  v_cnt NUMBER;
 BEGIN
  v_str := RPAD('select count(*) from emp',);
  EXECUTE IMMEDIATE v_str INTO v_cnt;
  dbms_output.put_line('v_cnt: '||v_cnt);
 END;
 /
DECLARE
*

SQL> DECLARE
  v_str LONG;
  v_cnt NUMBER;
 BEGIN
  v_str := RPAD('select count(*) from emp',);
  EXECUTE IMMEDIATE v_str INTO v_cnt;
  dbms_output.put_line('v_cnt: '||v_cnt);
 END;
 /
DECLARE
*

DECLARE 
 v_str CLOB;
 v_temp_str VARCHAR();
 v_cnt NUMBER;
 BEGIN
 dbms_lob.createtemporary(v_str,true);--创建一个临时lob
 v_temp_str := RPAD('select count(*) ',);
 dbms_lob.append(v_str,v_temp_str);--把临时字符串付给v_str
 v_temp_str := RPAD('from emp ',);
 dbms_lob.append(v_str,v_temp_str);--把临时字符串付给v_str
 EXECUTE IMMEDIATE v_str INTO v_cnt;
 dbms_output.put_line('v_cnt: '||v_cnt);
 dbms_lob.freetemporary(v_str);--释放lob
 END;