PostgreSQL data changes visibility rule: during a query execution, data changes made by the query itself (via SQL-function, SPI-function, triggers) are invisible to the query scan. For example, in query
INSERT INTO a SELECT * FROM a;
tuples inserted are invisible for SELECT scan. In effect, this duplicates the database table within itself (subject to unique index rules, of course) without recursing.
Changes made by query Q are visible by queries that are started after query Q, no matter whether they are started inside Q (during the execution of Q) or after Q is done.
This is true for triggers as well so, though a tuple being inserted (tg_trigtuple) is not visible to queries in a BEFORE trigger, this tuple (just inserted) is visible to queries in an AFTER trigger, and to queries in BEFORE/AFTER triggers fired after this!