只對部分行建立索引
創建大表:
create table t_big (id int,flag varchar2(5));
begin
for j in 0..100 loop
for i in 0..10000 loop
execute immediate 'insert into t_big(id) values(:1) ' using i;
end loop;
commit;
end loop;
end;
/
insert into t_big select r,case when mod(r,50)=0 then 'N' else 'Y' end from (select level r from dual connect by level<500);
commit;
創建索引
create index idx_flag on t_big(case flag when 'N' then 'N' end);
SQL> analyze index idx_flag validate structure;
Index analyzed.
SQL> select name,btree_space,lf_rows,height from index_stats;
NAME BTREE_SPACE LF_ROWS HEIGHT
------------------------------ ----------- ---------- ----------
IDX_FLAG 7996 9 1
使用:
select * from t_big where decode(flag,'N','N')='N';