All objects in a database need names.
This includes tables, columns, views, indexes, synonyms, sequences, users, roles, constraints, functions, and so on.
To enhance the readability of your SQL code, it is recommended that you restrict yourself to using the characters A through Z, the digits 0 through 9, and optionally the underscore (_).
In oracle, object names are case-insensitive; that is, internally all database object names are converted to uppercase, regardless of how you enter those names.
Database object names should always start with a letter.
Oracle object names have a maximum length of 30 characters.
Database objects need unique names within their namespace.