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Explicit Control Over Indexes when Creating, Disabling, or Dropping PK/Unique Constraints (Doc ID 139666.1)

Last updated on OCTOBER 24, 2023

Applies to:

Oracle Database - Enterprise Edition - Version 9.0.1.0 and later
Gen 1 Exadata Cloud at Customer (Oracle Exadata Database Cloud Machine) - Version N/A and later
Oracle Cloud Infrastructure - Database Service - Version N/A and later
Oracle Database Exadata Express Cloud Service - Version N/A and later
Oracle Database Cloud Exadata Service - Version N/A and later
Information in this document applies to any platform.

Purpose

PURPOSE
  In Oracle 9i, the DBA has an explicit control over how indexes are affected
  while creating, disabling, or dropping Primary Key (PK) and unique constraints.
  This bulletin explains the different behaviours of indexes associated with
  Primary Key or UNIQUE constraints according to the new clauses used when you 
  execute one of the following commands:
  
     CREATE TABLE ... PRIMARY KEY/UNIQUE
     ALTER TABLE  ... DISABLE PRIMARY KEY/UNIQUE
     ALTER TABLE  ... DROP PRIMARY KEY/UNIQUE
 

Scope

SCOPE & APPLICATION
  It is important for DBAs to know what happens to the indexes when creating,
  disabling or dropping a constraint relying on an index, since indexes may 
  have to be rebuilt after these operations. This can have two consequences:
 
    - Indexes may be missing for the Cost Based Optimizer (CBO) if the DBA 
      thinks that the index was not dropped. This can have a major impact on 
      performance.
    - Index rebuilding takes time.

Details

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