This question is common for all the database products I use, viz. SQL Server, MySQL, Oracle and PostgreSQL.
I have created a fresh database and the tables, at present, have no records. I have created indexes on all such columns of tables which are needed in queries often. I want to know how indexes are physically (clustered) and logically (non-clustered) updated when I keep on adding records in tables? Is the index updated automatically or do I need to update the indexes manually, from time-to-time?