Just for reference, even if there is no tns_names entry, we can use the complete connect string.
create database link MY_DBLINK connect to schema_user identified by pswd using '(DESCRIPTION =(ADDRESS_LIST =(ADDRESS =(COMMUNITY = tcp.world)(PROTOCOL = TCP)(Host = myserver.unix.myorg.org)(Port = 1521)))(CONNECT_DATA = (SID = MYDB_SID)))'
With tns entry: create database link MY_DBLINK connect to schema_user identified by pswd using 'TNS_CONNECT_ENTRY'
