Contain only letters (A-Z), digits (0-9), or the underscore character ( _ )
Not be reserved words, such as CREATE or DROP
Use ASCII characters only
SQL does not distinguish between uppercase and lowercase letters in SQL identifiers. It converts all names specified as conventional identifiers to uppercase, but statements can refer to the names in mixed case.
Example
The following example illustrates the use of identifiers in a simple query statement where CustNum, Order, and OrderDate are the user-specified names of columns:
SELECT CustNum, COUNT(*)
FROM Order
WHERE OrderDate < TO_DATE ('3/31/2004')
GROUP BY CustNum
HAVING COUNT (*) > 10 ;
Begin with an uppercase or lowercase letter