Queries Improvement in PostgreSQL 9.1
1. True serializable isolation level: Before version 9.1, PostgreSQL did not support a full serializable isolation level. A request for serializable transaction isolation actually provided snapshot isolation. This has well known anomalies which can allow inconsistent views of the data during concurrent transactions; although these anomalies only occur when certain patterns of read-write dependencies exist within a set of concurrent transactions. Where these patterns exist, the anomalies can be prevented by introducing conflicts through explicitly programmed locks or otherwise unnecessary writes to the database. Snapshot isolation is popular because performance is better than serializable isolation and the integrity guarantees which it does provide allow anomalies to be avoided or managed with reasonable effort in many environments. Following is a link on more details: http://wiki.postgresql.org/wiki/SSI 2. INSERT/UPDATE/DELETE in WITH CLAUSE. Now in 9.1, User would be able i