Write Skew anomaly in Oracle and PostgreSQL does not rollback transaction

Question

I noticed the following occurrence in both Oracle and PostgreSQL.

Considering we have the following database schema:

create table post (
    id int8 not          


        

Answer 1

I just wanted to point that Vlad Mihalcea's answer is plain wrong.

Is this a Phantom Read or a Write Skew?

Neither of those -- there is no anomaly here, transactions are serializable as Tx1 -> Tx2.

SQL standard states: "A serializable execution is defined to be an execution of the operations of concurrently executing SQL-transactions that produces the same effect as some serial execution of those same SQL-transactions."

PostgreSQL manages to catch this anomaly only if Bob issues a read against the employee table, otherwise the phenomenon is not prevented.

PostgreSQL's behavior here is 100% correct, it just "flips" apparent transactions order.