5
votes
1answer
86 views

Why does the CBO not chose a lower cost skip scan without stats?

In the script below, the CBO chooses an INDEX FAST FULL SCAN over an INDEX SKIP SCAN (this is illustrated by the queries with the UNION ALL but you can demonstrate it is true with just explain plan ...
14
votes
3answers
419 views

Oracle is not using a unique index for a long key

I have a table with 250K rows in my test database. (There are a few hundred millions in production, we can observe the same issue there.) The table has an nvarchar2(50) string identifier, not null, ...
0
votes
1answer
68 views

Oracle 11g INDEX_SS Hint

Given a table with columns A, B, and C of type CHAR(15) and an unique index If I have a query with a WHERE clause specifying A and C, oracle's optimizer chooses to do an index range scan. But if I ...