Creating an Oracle User if it doesn't already exist - oracle

Question

I am trying to create a script that will create users if they do not already exist.
CREATE USER "Kyle" PROFILE "DEFAULT" IDENTIFIED BY "password" ACCOUNT UNLOCK
WHERE NOT IN //Also tried 'WHERE NOT EXISTS'
(
SELECT username FROM all_users WHERE username = 'Kyle'
)
The following error is given:
SQL Error: ORA-00922: missing or invalid option
I was able to do this in SQL Server 2008 by using:
IF NOT EXISTS
(SELECT name FROM master.sys.server_principals
WHERE name = 'Kyle')
BEGIN
CREATE LOGIN Kyle WITH PASSWORD = 'temppassword' MUST_CHANGE, CHECK_EXPIRATION=ON, CHECK_POLICY=ON
END
Is there a similar way in Oracle to check if a user already exists before attempting to create a new user?

Answer 1

The IF NOT EXISTS syntax available in SQL Server, is not available in Oracle.
In general, Oracle scripts simply execute the CREATE statement, and if the object already exist, you'll get an error indicating that, which you can ignore. This is what all the standard Oracle deployment scripts do.
However, if you really want to check for existence, and only execute if object doesn't exist, thereby avoiding the error, you can code a PL/SQL block. Write a SQL that checks for user existence, and if it doesn't exist, use EXECUTE IMMEDIATE to do CREATE USER from the PL/SQL block.
An example of such a PL/SQL block might be:
declare
userexist integer;
begin
select count(*) into userexist from dba_users where username='SMITH';
if (userexist = 0) then
execute immediate 'create user smith identified by smith';
end if;
end;
/

Answer 2

You need to write a pl/sql block. See an example here
You can check if the user exists in the all_users table using some pl/sql code like:
SELECT count(*) INTO v_count_user
FROM all_users
WHERE username = 'Kyle'
and then use v_count_user in an IF condition to conditionally execute the create user statement.

Answer 3

From the previous answers, it is clear that if not exists is not supported in Oracle. To clarify which error(s) are thrown by Oracle when attempting to create an already existing user (and as a bonus, when attempting to drop a non existing user):
drop user foo;
ORA-01918: user 'foo' does not exist
create user existing_user IDENTIFIED BY existing_user;
ORA-01920: user name 'existing_user' conflicts with another user or role name
The statements above were executed on Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 - 64bit Production

Answer 4

Another way to do it is to create the user in a PL/SQL block and catch the ORA-01920 error. That way, the block does not throw any errors when the user exists.
DECLARE
sqlStatement varchar2(512);
user_exists EXCEPTION;
PRAGMA EXCEPTION_INIT(user_exists, -1920);
BEGIN
sqlStatement := 'CREATE USER "Kyle" ' ||
'IDENTIFIED BY "password" ' ||
'PROFILE "Default" ' ||
'ACCOUNT UNLOCK';
EXECUTE IMMEDIATE sqlStatement;
dbms_output.put_line(' OK: ' || sqlStatement);
EXCEPTION
WHEN user_exists THEN
dbms_output.put_line('WARN: ' || sqlStatement);
dbms_output.put_line('Already exists');
WHEN OTHERS THEN
dbms_output.put_line('FAIL: ' || sqlStatement);
RAISE;
END;
/