ORACLE Tips

• For typical day-to-day administrative tasks, it is recommended that you log in with the SYSTEM account. If you want to back up, recover, or upgrade the database, you must log in with the SYS account.
• PL/SQL treats any zero-length string like a NULL value. 
• When using NULL values, remember the following rules:
  ■ Comparisons involving NULL values always yield NULL.
  ■ Applying the logical operator NOT to a NULL value yields NULL.
  ■ In conditional control statements, if the condition yields NULL, its associated
  sequence of statements is not executed.
  ■ If the expression in a simple CASE statement or CASE expression yields NULL, it
  cannot be matched by using WHEN NULL. Instead, use a searched CASE syntax with
  WHEN expression IS NULL.
• The concatenation operator ignores null operands