哪些表的索引个数过多：
prompt <p>当前用户下,哪些表的索引个数字超过5个的 select table_name, count(*) cnt from user_indexes group by table_name having count(*) >= 5 order by cnt desc ;
哪些表的外键未建索引：
prompt <p>将外键未建索引的情况列出
select table_name,
constraint_name,
cname1 || nvl2(cname2, ',' || cname2, null) ||
nvl2(cname3, ',' || cname3, null) ||
nvl2(cname4, ',' || cname4, null) ||
nvl2(cname5, ',' || cname5, null) ||
nvl2(cname6, ',' || cname6, null) ||
nvl2(cname7, ',' || cname7, null) ||
nvl2(cname8, ',' || cname8, null) columns
from (select b.table_name,
b.constraint_name,
max(decode(position, 1, column_name, null)) cname1,
max(decode(position, 2, column_name, null)) cname2,
max(decode(position, 3, column_name, null)) cname3,
max(decode(position, 4, column_name, null)) cname4,
max(decode(position, 5, column_name, null)) cname5,
max(decode(position, 6, column_name, null)) cname6,
max(decode(position, 7, column_name, null)) cname7,
max(decode(position, 8, column_name, null)) cname8,
count(*) col_cnt
from (select substr(table_name, 1, 30) table_name,
substr(constraint_name, 1, 30) constraint_name,
substr(column_name, 1, 30) column_name,
position
from user_cons_columns) a,
user_constraints b
where a.constraint_name = b.constraint_name
and b.constraint_type = 'R'
group by b.table_name, b.constraint_name) cons
where col_cnt > ALL
(select count(*)
from user_ind_columns i
where i.table_name = cons.table_name
and i.column_name in (cname1, cname2, cname3, cname4, cname5,
cname6, cname7, cname8)
and i.column_position <= cons.col_cnt
group by i.index_name);
哪些表组合索引列过多
prompt <p>当前用户下，哪些组合索引组合列超过4个的 select table_name, index_name, count(*) from user_ind_columns group table_name, index_name having count(*) >= 4 order by count(*) desc;
哪些大表未建任何索引
--针对普通表（大于2GB的表未建任何索引） select segment_name, bytes/1024/1024/1024 "GB", blocks, tablespace_name from user_segments where segment_type = 'TABLE' and segment_name not in (select table_name from user_indexes) and bytes / 1024 / 1024 / 1024 >= 2 order by GB desc; --针对分区表（大于2GB的分区表未建任何索引） --无论是建了局部索引还是全局索引，在user_indexes都可以查到，只是status不一样。 select segment_name, sum(bytes)/1024/1024/1024 "GB", sum(blocks) from user_segments where segment_type = 'TABLE PARTITION' and segment_name not in (select table_name from user_indexes) group by segment_name having sum(bytes)/1024/1024/1024>=2 order by GB desc; --注：无论是建了局部索引还是全局索引，在user_indexes都可以查到，只是status不一样。
哪些聚索引列合因子差
prompt <p>当前用户下，哪些索引的聚合因子特别大。
select a.table_name,
a.index_name,
a.blevel,
a.leaf_blocks,
b.num_rows,
b.blocks,
a.clustering_factor,
trunc(a.clustering_factor / b.num_rows,2) cluster_rate
from user_indexes a, user_tables b
where a.table_name = b.table_name
and a.clustering_factor is not null
and a.clustering_factor / b.num_rows>0.9
order by cluster_rate desc ;
哪些类型的索引已失效
prompt <p>失效-普通索引
select t.index_name,
t.table_name,
blevel,
t.num_rows,
t.leaf_blocks,
t.distinct_keys
from user_indexes t
where status = 'UNUSABLE' ;
prompt <p>失效-分区索引
select t1.blevel,
t1.leaf_blocks,
t1.INDEX_NAME,
t2.table_name,
t1.PARTITION_NAME,
t1.STATUS
from user_ind_partitions t1, user_indexes t2
where t1.index_name = t2.index_name
and t1.STATUS = 'UNUSABLE';
哪些索引单列组合有叉
prompt <p>当前用户下，哪些表的组合索引与单列索引存在交叉的情况。 select table_name, trunc(count(distinct(column_name)) / count(*),2) cross_idx_rate from user_ind_columns group by table_name having count(distinct(column_name)) / count(*) < 1 order by cross_idx_rate desc; ---------例子 drop table t purge; drop table t1 purge; create table t1 as select * from dba_objects where object_id is not null; create index idx_t1_objid_owner on t1(object_id ,owner); create index idx_t1_object_id on t1(object_id ); drop table t2 purge; create table t2 as select * from dba_objects where object_id is not null; create index idx_t2_objid_owner on t2(object_id,owner); create index idx_t2_object_id on t2(object_id); create index idx_t2_owner on t2(owner); drop table t3 purge; create table t3 as select * from dba_objects where object_id is not null; create index idx_t3_objid_owner on t3(object_id,owner); create index idx_t3_owner_objid on t3(owner,object_id); create index idx_t3_object_id on t3(object_id); create index idx_t3_owner on t3(owner); ---执行如下语句，发现当前用户下，T3,T2,T1表存在索引单列组合有交叉，最严重的是T3 select table_name, trunc(count(distinct(column_name)) / count(*),2) cross_idx_rate from user_ind_columns group by table_name having count(distinct(column_name)) / count(*) < 1 order by cross_idx_rate ; TABLE_NAME CROSS_IDX_RATE ------------------------------ -------------- T3 .33 T2 .5 T1 .66
哪些索引的高度比较高
prompt <p>当前用户下，哪些索引的高度比较高，大于5层（LEVEL=4)
select table_name,
index_name,
blevel,
leaf_blocks,
num_rows,
last_analyzed,
degree,
status
from user_indexes
where blevel>=4;
哪些索引建后从未使用
prompt <p>当前用户下，哪些索引最近30天内从未被使用过。 set linesize 166 col INDEX_NAME for a10 col TABLE_NAME for a10 col MONITORING for a10 col USED for a10 col START_MONITORING for a25 col END_MONITORING for a25 --以下判断在最近30天内未被使用过的索引有哪些 select * from v$object_usage where USED = 'NO' and START_MONITORING <= sysdate - 30 and END_MONITORING is not null; --注，之前需有对索引进行监控，如 alter index idx_t_id monitoring usage; ---如果取消监控就是 alter index idx_t_id nomonitoring usage;
哪些索引设置并行属性
prompt <p>当前用户下，哪些索引被设置了并行。
select table_name,
index_name,
blevel,
leaf_blocks,
num_rows,
last_analyzed,
degree,
status
from user_indexes
where degree>1;
哪些索引统计信息太旧
--普通索引（从未收集过统计信息或者是最近10天内未收集过统计信息的表）
select index_name, table_name, last_analyzed, num_rows, temporary, status
from user_indexes
where status <> 'N/A'
and (last_analyzed is null or last_analyzed < sysdate - 10);
--分区索引（从未收集过统计信息或者是最近10天内未收集过统计信息的分区）
select t2.table_name,
t1.INDEX_NAME,
t1.PARTITION_NAME,
t1.last_analyzed,
t1.blevel,
t1.leaf_blocks,
t1.STATUS
from user_ind_partitions t1, user_indexes t2
where t1.index_name = t2.index_name
and (t1.last_analyzed is null or t1.last_analyzed < sysdate - 10);
哪些主外键约束失效了
prompt <p>当前用户下，哪些外键的约束失效了。
SELECT TABLE_NAME,
CONSTRAINT_NAME,
STATUS,
CONSTRAINT_TYPE,
R_CONSTRAINT_NAME
FROM USER_CONSTRAINTS
WHERE STATUS='DISABLED';
--试验
drop table t_p cascade constraints purge;
drop table t_c cascade constraints purge;
CREATE TABLE T_P (ID NUMBER, NAME VARCHAR2(30));
ALTER TABLE T_P ADD CONSTRAINT T_P_ID_PK PRIMARY KEY (ID);
CREATE TABLE T_C (ID NUMBER, FID NUMBER, NAME VARCHAR2(30));
ALTER TABLE T_C ADD CONSTRAINT FK_T_C FOREIGN KEY (FID) REFERENCES T_P (ID);
set autotrace off
INSERT INTO T_P SELECT ROWNUM, TABLE_NAME FROM ALL_TABLES;
INSERT INTO T_C SELECT ROWNUM, MOD(ROWNUM, 1000) + 1, OBJECT_NAME FROM ALL_OBJECTS;
COMMIT;
ALTER TABLE T_C DISABLE CONSTRAINT FK_T_C;
CREATE INDEX IND_T_C_FID ON T_C (FID);
来源：https://www.cnblogs.com/sunliyuan/p/12366336.html