查看统计信息是否过期：
DML 超过了 10% 都会过期
exec dbms_stats.flush_database_monitoring_info;
select owner, table_name name, object_type, stale_stats, last_analyzed
from dba_tab_statistics
where owner = 'SCOTT'
and table_name in ('TEST')
and (stale_stats = 'YES' or last_analyzed is null);