What is the difference between USER() and SYS_CONTEXT('USERENV','CURRENT_USER')?

Question

In an Oracle Database, what are the differences between the following:

• user()
• sys_context(\'USERENV\', \'CURRENT_USER\')
• sys_context(\'USEREN

Answer 1

There is also a performance difference between USER and using sys_context

declare 
  v_result varchar2(100);
begin
  for i in 1..1000000 loop
  v_result := sys_context('userenv','session_user');
  end loop;
end;
/

-- 2.5s

declare 
  v_result varchar2(100);
begin
  for i in 1..1000000 loop
  v_result := user;
  end loop;
end;
/ 

-- 47s

Also see https://svenweller.wordpress.com/2016/02/24/sequence-and-audit-columns-with-apex-5-and-12c/ and http://www.grassroots-oracle.com/2019/01/oracle-user-vs-sys-context.html