什么原因导致统计信息失效--SQL

select *
from (select *
from (select *
from (select u.name owner,
o.name table_name,
null partition_name,
null subpartition_name,
m.inserts,
m.updates,
m.deletes,
m.timestamp,
decode(bitand(m.flags, 1), 1, 'YES', 'NO') truncated,
m.drop_segments
from sys.mon_mods_all$ m,
sys.obj$ o,
sys.tab$ t,
sys.user$ u
where o.obj# = m.obj#
and o.obj# = t.obj#
and o.owner# = u.user#
union all
select u.name,
o.name,
o.subname,
null,
m.inserts,
m.updates,
m.deletes,
m.timestamp,
decode(bitand(m.flags, 1), 1, 'YES', 'NO'),
m.drop_segments
from sys.mon_mods_all$ m, sys.obj$ o, sys.user$ u
where o.owner# = u.user#
and o.obj# = m.obj#
and o.type# = 19
union all
select u.name,
o.name,
o2.subname,
o.subname,
m.inserts,
m.updates,
m.deletes,
m.timestamp,
decode(bitand(m.flags, 1), 1, 'YES', 'NO'),
m.drop_segments
from sys.mon_mods_all$ m,
sys.obj$ o,
sys.tabsubpart$ tsp,
sys.obj$ o2,
sys.user$ u
where o.obj# = m.obj#
and o.owner# = u.user#
and o.obj# = tsp.obj#
and o2.obj# = tsp.pobj#)
where owner not like '%SYS%'
and owner not like 'XDB'
union all
select *
from (select u.name owner,
o.name table_name,
null partition_name,
null subpartition_name,
m.inserts,
m.updates,
m.deletes,
m.timestamp,
decode(bitand(m.flags, 1), 1, 'YES', 'NO') truncated,
m.drop_segments
from sys.mon_mods$ m,
sys.obj$ o,
sys.tab$ t,
sys.user$ u
where o.obj# = m.obj#
and o.obj# = t.obj#
and o.owner# = u.user#
union all
select u.name,
o.name,
o.subname,
null,
m.inserts,
m.updates,
m.deletes,
m.timestamp,
decode(bitand(m.flags, 1), 1, 'YES', 'NO'),
m.drop_segments
from sys.mon_mods$ m, sys.obj$ o, sys.user$ u
where o.owner# = u.user#
and o.obj# = m.obj#
and o.type# = 19
union all
select u.name,
o.name,
o2.subname,
o.subname,
m.inserts,
m.updates,
m.deletes,
m.timestamp,
decode(bitand(m.flags, 1), 1, 'YES', 'NO'),
m.drop_segments
from sys.mon_mods$ m,
sys.obj$ o,
sys.tabsubpart$ tsp,
sys.obj$ o2,
sys.user$ u
where o.obj# = m.obj#
and o.owner# = u.user#
and o.obj# = tsp.obj#
and o2.obj# = tsp.pobj#)
where owner not like '%SYS%'
and owner not like '%XDB%')
order by inserts desc)
where rownum <= 50;