SQL duplicate rows with reference to other table - sql

Question

I have two tables which are designed like this.
CREATE TABLE employee
(
id INT PRIMARY KEY,
name VARCHAR(200)
);
CREATE TABLE job
(
id INT PRIMARY KEY,
name VARCHAR(200),
emp_id INT,
FOREIGN KEY (emp_id) REFERENCES employee(id)
);
insert into employee (id, name) values (1, 'user1');
insert into employee (id, name) values (2, 'user2');
insert into employee (id, name) values (3, 'user3');
insert into job (id, name, emp_id) values (1, 'job1', 1);
insert into job (id, name, emp_id) values (2, 'job2', 2);
insert into job (id, name, emp_id) values (3, 'job3', 3);
insert into job (id, name, emp_id) values (4, 'job3', 3);
And what I need is
a query
to duplicate user1,2,3 into 4,5,6, but meanwhile, a old set of job 1,2,3,4 that are referenced with user 1,2,3 will be copied as job 5,6,7,8 and the new user 4,5,6 will have reference to the new 5,6,7,8.
So the result before the query.
Job Table:
id name emp_id
1 t_job1 1
2 t_job2 2
3 t_job3 3
4 t_job3 3
Employee table:
id name
1 user1
2 user2
3 user3
After running the query for duplicating user1,2,3:
Job Table:
id name emp_id
1 t_job1 1
2 t_job2 2
3 t_job3 3
4 t_job3 3
5 t_job1 4
6 t_job2 5
7 t_job3 6
8 t_job3 6
Employee table:
id name
1 user1
2 user2
3 user3
4 user1
5 user2
6 user3
This is an ideal case, but in the code we really work on, there is indefinite amount of job and employee relationship.
So how could this be achieved with query?
For one thing, I cannot change the table structure, if I could, I would.
Attach the link:
http://sqlfiddle.com/#!9/de15f/1
We are using oracle, but I put the example under MySQL.

Answer 1

As mentioned above, the answer may depend on the database system that's being used. Below mentioned is a working code built for SQL Server. Hope this helps. :-)
DECLARE #NewEmployee AS TABLE (id INT, [name] VARCHAR(200));
DECLARE #NewJob AS TABLE (id INT, [name] VARCHAR(200), emp_id INT);
DECLARE #Max INT, #i INT = 0;
INSERT INTO #NewEmployee (id, [name])
SELECT e.id + m.MaxId, e.[name]
FROM employee e
CROSS APPLY(SELECT max(id) MaxId FROM employee) m;
INSERT #NewJob (id, [name])
SELECT J.id + m.MaxId id, J.[name]
FROM job j
CROSS APPLY(SELECT max(id) MaxId FROM job) m;
SELECT #Max = MAX(id), #i = MAX(id) - COUNT(1) + 1 FROM #NewJob;
WHILE #i <= #Max
BEGIN
UPDATE nj
SET nj.emp_id = ISNULL(ne.id, me.id)
FROM #NewJob nj
CROSS APPLY (SELECT MIN(id) id FROM
( SELECT e.id id FROM #NewEmployee e
EXCEPT
SELECT emp_id id FROM #NewJob) T) ne
CROSS APPLY (SELECT MAX(e.id) id FROM #NewEmployee e) me
WHERE nj.id = #i
SET #i = #i + 1;
END;
INSERT INTO employee
SELECT * FROM #NewEmployee;
INSERT INTO job
SELECT * FROM #NewJob;
SELECT * FROM employee;
SELECT * FROM job;