Oracle 18c

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SELECT * FROM v$version;


BANNER
BANNER_FULL
BANNER_LEGACY
CON_ID


Oracle Database 18c Express Edition Release 18.0.0.0.0 - Production
Oracle Database 18c Express Edition Release 18.0.0.0.0 - Production
Version 18.4.0.0.0
Oracle Database 18c Express Edition Release 18.0.0.0.0 - Production
0


CREATE TABLE user_ -- Oracle doesn't let you create a table called "user"
(
  user_id INTEGER NOT NULL PRIMARY KEY,
  user_name VARCHAR (25) NOT NULL  
);
INSERT INTO user_ (user_id, user_name)
SELECT 1, 'user_1' FROM dual
UNION
SELECT 2, 'user_2' FROM dual;


2 rows affected

SELECT * FROM user_ ORDER BY user_id;


USER_ID
USER_NAME


1
user_1

2
user_2


CREATE TABLE message
(
  message_id INTEGER NOT NULL PRIMARY KEY,
  sender_id INTEGER,
  message_text VARCHAR (100) NOT NULL,
  FOREIGN KEY (sender_id) REFERENCES user_ (user_id)
);
INSERT INTO message 
SELECT 1, 1, 'm1' FROM dual 
UNION 
SELECT 2, 1, 'm2' FROM dual
UNION 
SELECT 3, 2, 'm3' FROM dual
UNION 
SELECT 4, 2, 'm4' FROM dual;
4 rows affected

SELECT * FROM message;


MESSAGE_ID
SENDER_ID
MESSAGE_TEXT


1
1
m1

2
1
m2

3
2
m3

4
2
m4


INSERT INTO message VALUES (5, 56, 'mxxxx');
ORA-02291: integrity constraint (FIDDLE_HZJYYUHEPWQHPRXCKACI.SYS_C0032739) violated - parent key not found