Create unique index in oracle

Siebel Analytics Performance Tuning Guide > The Database Servers > Index Selection >

B-Tree Indexes

Generally speaking, in an online transaction processing environment, a B-tree is most effective when it is highly selective.

When this is the case, the index is said to have "high selectivity" because a low percentage of rows in the table have the same index key value.

General Guidelines

With high selectivity in mind, evaluate creating B-tree indexes on columns that:

• Occur frequently in WHERE clauses
• Often used to join tables (include aggregate tables)
• Occur in ORDER BY clauses (the index can facilitate ordering)
• Occur in a foreign key reference constraint
• Used to enforce PRIMARY KEY and UNIQUENESS constraints

You can also look at your query workload and identify families of queries that include tight table constraints on tables (point, multi-point, and range queries).

When you have star schemas, both DB2 and Oracle database servers can exploit multi-column B-Tree indexes to accelerate join processing when they are created over the foreign