I did the following with 18.1. Created a basic diagram
Then did a DDL export and got this (keeping with all defaults)
-- Generated by Oracle SQL Developer Data Modeler 18.1.0.082.1035
-- at: 2019-11-11 09:48:27 AWST
-- site: Oracle Database 11g
-- type: Oracle Database 11g
CREATE user scott identified by account unlock
;
CREATE TABLE scott.dept (
deptno NUMBER(2) NOT NULL,
dname VARCHAR2(14 BYTE),
loc VARCHAR2(13 BYTE)
)
PCTFREE 10 PCTUSED 40 TABLESPACE users LOGGING
STORAGE ( INITIAL 65536 NEXT 1048576 PCTINCREASE 0 MINEXTENTS 1 MAXEXTENTS 2147483645 FREELISTS 1 FREELIST GROUPS 1 BUFFER_POOL DEFAULT );
CREATE UNIQUE INDEX scott.dept_pk ON
scott.dept (
deptno
ASC )
TABLESPACE users PCTFREE 10
STORAGE ( INITIAL 65536 NEXT 1048576 PCTINCREASE 0 MINEXTENTS 1 MAXEXTENTS 2147483645 FREELISTS 1 FREELIST GROUPS 1 BUFFER_POOL DEFAULT )
LOGGING;
ALTER TABLE scott.dept
ADD CONSTRAINT dept_pk PRIMARY KEY ( deptno )
USING INDEX scott.dept_pk;
CREATE TABLE scott.emp (
empno NUMBER(4) NOT NULL,
ename VARCHAR2(10 BYTE),
job VARCHAR2(9 BYTE),
mgr NUMBER(4),
hiredate DATE,
sal NUMBER(7,2),
comm NUMBER(7,2),
deptno NUMBER(2)
)
PCTFREE 10 PCTUSED 40 TABLESPACE users LOGGING
STORAGE ( INITIAL 65536 NEXT 1048576 PCTINCREASE 0 MINEXTENTS 1 MAXEXTENTS 2147483645 FREELISTS 1 FREELIST GROUPS 1 BUFFER_POOL DEFAULT );
CREATE UNIQUE INDEX scott.emp_pk ON
scott.emp (
empno
ASC )
TABLESPACE users PCTFREE 10
STORAGE ( INITIAL 65536 NEXT 1048576 PCTINCREASE 0 MINEXTENTS 1 MAXEXTENTS 2147483645 FREELISTS 1 FREELIST GROUPS 1 BUFFER_POOL DEFAULT )
LOGGING;
ALTER TABLE scott.emp
ADD CONSTRAINT emp_pk PRIMARY KEY ( empno )
USING INDEX scott.emp_pk;
ALTER TABLE scott.emp
ADD CONSTRAINT emp_fk FOREIGN KEY ( deptno )
REFERENCES scott.dept ( deptno )
NOT DEFERRABLE;
-- Oracle SQL Developer Data Modeler Summary Report:
--
-- CREATE TABLE 2
-- CREATE INDEX 2
-- ALTER TABLE 3
-- CREATE VIEW 0
-- ALTER VIEW 0
-- CREATE PACKAGE 0
-- CREATE PACKAGE BODY 0
-- CREATE PROCEDURE 0
-- CREATE FUNCTION 0
-- CREATE TRIGGER 0
-- ALTER TRIGGER 0
-- CREATE COLLECTION TYPE 0
-- CREATE STRUCTURED TYPE 0
-- CREATE STRUCTURED TYPE BODY 0
-- CREATE CLUSTER 0
-- CREATE CONTEXT 0
-- CREATE DATABASE 0
-- CREATE DIMENSION 0
-- CREATE DIRECTORY 0
-- CREATE DISK GROUP 0
-- CREATE ROLE 0
-- CREATE ROLLBACK SEGMENT 0
-- CREATE SEQUENCE 0
-- CREATE MATERIALIZED VIEW 0
-- CREATE SYNONYM 0
-- CREATE TABLESPACE 0
-- CREATE USER 1
--
-- DROP TABLESPACE 0
-- DROP DATABASE 0
--
-- REDACTION POLICY 0
--
-- ORDS DROP SCHEMA 0
-- ORDS ENABLE SCHEMA 0
-- ORDS ENABLE OBJECT 0
--
-- ERRORS 0
-- WARNINGS 0
Maybe as Jeff suggested - throw this onto the forum with some screen dumps and we can see where things are different for you