sys_context returns the value of parameter associated with the context namespace. You can use this function in both SQL and PL/SQL statements.
For namespace and parameter, you can specify either a string (constant) or an expression that resolves to a string designating a namespace or an attribute. The context namespace must already have been created, and the associated parameter and its value must also have been set using the DBMS_SESSION.set_context procedure. The namespace must be a valid SQL identifier. The parameter name can be any string. It is not case sensitive, but it cannot exceed 30 bytes in length.
The datatype of the return value is VARCHAR2. The default maximum size of the return value is 256 bytes. You can override this default by specifying the optional length parameter. The valid range of values is 1 to 4000 bytes. (If you specify an invalid value, then Oracle ignores it and uses the default.)