You're right, Postgres wraps every statement in an implicit transaction. The point of that first example is that the SELECT and UPDATE are in separate auto-committed transactions - there's no explicit transaction block wrapping both. So another connection can change the value between your SELECT and your UPDATE.
Comments
You're right, Postgres wraps every statement in an implicit transaction. The point of that first example is that the SELECT and UPDATE are in separate auto-committed transactions - there's no explicit transaction block wrapping both. So another connection can change the value between your SELECT and your UPDATE.