存储过程中使用EXECUTE IMMEDIATE提示权限不足，可是单独执行sql没有问题！

存储过程中使用EXECUTE IMMEDIATE提示权限不足，可是单独执行sql没有问题！

v_sql :=
' create table '
|| i_table
|| ' TABLESPACE '
|| i_table_ts
|| ' PARTITION BY RANGE (REGION_ID) '
|| ' ( '
|| ' PARTITION A VALUES LESS THAN (''B''), '
|| ' PARTITION B VALUES LESS THAN (''C''), '
|| ' PARTITION C VALUES LESS THAN (''D''), '
|| ' PARTITION D VALUES LESS THAN (''E''), '
|| ' PARTITION E VALUES LESS THAN (''F''), '
|| ' PARTITION F VALUES LESS THAN (''G''), '
|| ' PARTITION G VALUES LESS THAN (''H''), '
|| ' PARTITION H VALUES LESS THAN (''I''), '
|| ' PARTITION I VALUES LESS THAN (''J''), '
|| ' PARTITION J VALUES LESS THAN (''K''), '
|| ' PARTITION K VALUES LESS THAN (''L''), '
|| ' PARTITION L VALUES LESS THAN (''M''), '
|| ' PARTITION M VALUES LESS THAN (maxvalue) '
|| ' ) '
|| ' as select * from '
|| i_table_last
|| ' where 1=2 ';

EXECUTE IMMEDIATE v_sql;

请问这是为什么？