CDB中只能创建c##全局用户，而PDB中才可创建普通用户，且普通用户连接PDB需要用tns方式连接。
CDB中：
create user c##user1 identified by password;
grant resource,connect to c##user1;
[oracle@rhel75 admin]$ sqlplus c##user1/password
SQL*Plus: Release 19.0.0.0.0 - Production on Sun Apr 26 05:02:38 2020
Version 19.3.0.0.0
Copyright (c) 1982, 2019, Oracle. All rights reserved.
Last Successful login time: Sun Apr 26 2020 04:58:44 -04:00
Connected to:
Oracle Database 19c Enterprise Edition Release 19.0.0.0.0 - Production
Version 19.3.0.0.0
C##USER1@orcl19c>
PDB中：
create user puser1 identified by password;
grant resource,connect to puser1;
[oracle@rhel75 admin]$ sqlplus puser1/password@PORCL
SQL*Plus: Release 19.0.0.0.0 - Production on Sun Apr 26 05:02:59 2020
Version 19.3.0.0.0
Copyright (c) 1982, 2019, Oracle. All rights reserved.
Last Successful login time: Sun Apr 26 2020 04:59:39 -04:00
Connected to:
Oracle Database 19c Enterprise Edition Release 19.0.0.0.0 - Production
Version 19.3.0.0.0
PUSER1@PORCL