Oracle creates index for primary key in snapshot base table - Oracle Replication

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• Nirja Shah   -Posted on 01 Oct 15
  - Primary key snapshots are the default type of snapshot.
  
  - They are updateable if the snapshot was created as part of a snapshot group and "FOR UPDATE" was specified when defining the snapshot.
  
  - Changes are propagated according to the row-level changes that have occurred, as identified by the primary key value of the row (not the ROWID).
  
  - The SQL statement for creating an updateable, primary key snapshot might look like:
  
  CREATE SNAPSHOT sales.customer FOR UPDATE AS
  SELECT * FROM sales.customer@dbs1.acme.com;
  
  - Primary key snapshots may contain a subquery so that you can create a horizontally partitioned subset of data at the remote snapshot site.
  
  - This subquery may be as simple as a basic WHERE clause or as complex as a multilevel WHERE EXISTS clause.
  
  - Primary key snapshots that contain a selected class of subqueries can still be incrementally or fast refreshed.
  
  - The following is a subquery snapshot with a WHERE clause containing a subquery:
  
  CREATE SNAPSHOT sales.orders REFRESH FAST AS
  SELECT * FROM sales.orders@dbs1.acme.com o
  WHERE EXISTS
  (SELECT 1 FROM sales.customer@dbs1.acme.com c
  WHERE o.c_id = c.c_id AND zip = 19555);

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