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==Maintenance of the referential constraint==



<source lang="sql">

28>
29> CREATE TABLE works_on (emp_no INTEGER NOT NULL,
30> project_no CHAR(4) NOT NULL,
31> job CHAR (15) NULL,
32> enter_date DATETIME NULL)
33>
34> insert into works_on values (1, "p1", "analyst", "1997.10.1")
35> insert into works_on values (1, "p3", "manager", "1999.1.1")
36> insert into works_on values (2, "p2", "clerk", "1998.2.15")
37> insert into works_on values (2, "p2", NULL, "1998.6.1")
38> insert into works_on values (3, "p2", NULL, "1997.12.15")
39> insert into works_on values (4, "p3", "analyst", "1998.10.15")
40> insert into works_on values (5, "p1", "manager", "1998.4.15")
41> insert into works_on values (6, "p1", NULL, "1998.8.1")
42> insert into works_on values (7, "p2", "clerk", "1999.2.1")
43> insert into works_on values (8, "p3", "clerk", "1997.11.15")
44> insert into works_on values (7, "p1", "clerk", "1998.1.4")
45>
46> select * from works_on
47> GO
(1 rows affected)
(1 rows affected)
(1 rows affected)
(1 rows affected)
(1 rows affected)
(1 rows affected)
(1 rows affected)
(1 rows affected)
(1 rows affected)
(1 rows affected)
(1 rows affected)
emp_no project_no job enter_date
----------- ---------- --------------- -----------------------
1 p1 analyst 1997-10-01 00:00:00.000
1 p3 manager 1999-01-01 00:00:00.000
2 p2 clerk 1998-02-15 00:00:00.000
2 p2 NULL 1998-06-01 00:00:00.000
3 p2 NULL 1997-12-15 00:00:00.000
4 p3 analyst 1998-10-15 00:00:00.000
5 p1 manager 1998-04-15 00:00:00.000
6 p1 NULL 1998-08-01 00:00:00.000
7 p2 clerk 1999-02-01 00:00:00.000
8 p3 clerk 1997-11-15 00:00:00.000
7 p1 clerk 1998-01-04 00:00:00.000
(11 rows affected)
1> CREATE TABLE employee (emp_no INTEGER NOT NULL,
2> emp_fname CHAR(20) NOT NULL,
3> emp_lname CHAR(20) NOT NULL,
4> dept_no CHAR(4) NULL)
5>
6> insert into employee values(1, "Matthew", "Smith", "d3")
7> insert into employee values(2, "Ann", "Jones", "d3")
8> insert into employee values(3, "John", "Barrimore","d1")
9> insert into employee values(4, "James", "James", "d2")
10> insert into employee values(5, "Elsa", "Bertoni", "d2")
11> insert into employee values(6, "Elke", "Hansel", "d2")
12> insert into employee values(7, "Sybill", "Moser", "d1")
13>
14> select * from employee
15> GO
(1 rows affected)
(1 rows affected)
(1 rows affected)
(1 rows affected)
(1 rows affected)
(1 rows affected)
(1 rows affected)
emp_no emp_fname emp_lname dept_no
----------- -------------------- -------------------- -------
1 Matthew Smith d3
2 Ann Jones d3
3 John Barrimore d1
4 James James d2
5 Elsa Bertoni d2
6 Elke Hansel d2
7 Sybill Moser d1
(7 rows affected)
1>
2> -- Maintenance of the referential constraint
3>
4> CREATE PROCEDURE delete_emp @employee_no INT, @counter INT OUTPUT
5> AS SELECT @counter = COUNT(*) FROM works_on WHERE emp_no = @employee_no
6> DELETE FROM employee WHERE emp_no = @employee_no
7> DELETE FROM works_on WHERE emp_no = @employee_no
8> GO
1>
2> DECLARE @C int
3> EXEC delete_emp 1, @C
4> Print @C
5> GO
(1 rows affected)
(2 rows affected)
(2 rows affected)
1>
2> select * from employee
3> select * from works_on
4> GO
emp_no emp_fname emp_lname dept_no
----------- -------------------- -------------------- -------
2 Ann Jones d3
3 John Barrimore d1
4 James James d2
5 Elsa Bertoni d2
6 Elke Hansel d2
7 Sybill Moser d1
(6 rows affected)
emp_no project_no job enter_date
----------- ---------- --------------- -----------------------
2 p2 clerk 1998-02-15 00:00:00.000
2 p2 NULL 1998-06-01 00:00:00.000
3 p2 NULL 1997-12-15 00:00:00.000
4 p3 analyst 1998-10-15 00:00:00.000
5 p1 manager 1998-04-15 00:00:00.000
6 p1 NULL 1998-08-01 00:00:00.000
7 p2 clerk 1999-02-01 00:00:00.000
8 p3 clerk 1997-11-15 00:00:00.000
7 p1 clerk 1998-01-04 00:00:00.000
(9 rows affected)
1>
2>
3> drop procedure delete_emp
4> drop table employee
5> drop table works_on
6> GO
1>
2>

</source>

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