Note About SQL Functions

SQL Functions

SQL functions are built into Oracle and are available for use in various appropriate
SQL statements. Do not confuse SQL functions with user functions written in
PL/SQL.

If you call a SQL function with an argument of a datatype other than the datatype expected by the SQL function, then Oracle implicitly converts the argument to the expected datatype before performing the SQL function. If you call a SQL function with a null argument, then the SQL function automatically returns null. The only SQL functions that do not necessarily follow this behavior are CONCAT, NVL, and REPLACE.
In the syntax diagrams for SQL functions, arguments are indicated by their datatypes. When the parameter "function" appears in SQL syntax, replace it with one of the functions described in this section. Functions are grouped by the datatypes of their arguments and their return values.

Note: When you apply SQL functions to LOB columns, Oracle
creates temporary LOBs during SQL and PL/SQL processing. You
should ensure that temporary tablespace quota is sufficient for
storing these temporary LOBs for your application.