EXISTS Function and Subqueries
17>
18> CREATE TABLE employee (emp_no INTEGER NOT NULL,
19> emp_fname CHAR(20) NOT NULL,
20> emp_lname CHAR(20) NOT NULL,
21> dept_no CHAR(4) NULL)
22>
23> insert into employee values(1, 'Matthew', 'Smith', 'd3')
24> insert into employee values(2, 'Ann', 'Jones', 'd3')
25> insert into employee values(3, 'John', 'Barrimore','d1')
26> insert into employee values(4, 'James', 'James', 'd2')
27> insert into employee values(5, 'Elsa', 'Bertoni', 'd2')
28> insert into employee values(6, 'Elke', 'Hansel', 'd2')
29> insert into employee values(7, 'Sybill', 'Moser', 'd1')
30>
31> select * from employee
32> 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> CREATE TABLE works_on (emp_no INTEGER NOT NULL,
3> project_no CHAR(4) NOT NULL,
4> job CHAR (15) NULL,
5> enter_date DATETIME NULL)
6>
7> insert into works_on values (1, 'p1', 'analyst', '1997.10.1')
8> insert into works_on values (1, 'p3', 'manager', '1999.1.1')
9> insert into works_on values (2, 'p2', 'clerk', '1998.2.15')
10> insert into works_on values (2, 'p2', NULL, '1998.6.1')
11> insert into works_on values (3, 'p2', NULL, '1997.12.15')
12> insert into works_on values (4, 'p3', 'analyst', '1998.10.15')
13> insert into works_on values (5, 'p1', 'manager', '1998.4.15')
14> insert into works_on values (6, 'p1', NULL, '1998.8.1')
15> insert into works_on values (7, 'p2', 'clerk', '1999.2.1')
16> insert into works_on values (8, 'p3', 'clerk', '1997.11.15')
17> insert into works_on values (7, 'p1', 'clerk', '1998.1.4')
18>
19> select * from works_on
20> 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> -- EXISTS Function and Subqueries
2>
3> -- EXISTS function takes a subquery as an argument and returns true if the subquery returns one or more rows, and it returns false if the subquery returns zero rows.
4>
5> SELECT emp_lname FROM employee WHERE EXISTS
6> (SELECT * FROM works_on WHERE employee.emp_no = works_on.emp_no AND project_no='p1')
7>
8> drop table works_on
9> drop table employee
10> GO
emp_lname
--------------------
Smith
Bertoni
Hansel
Moser
(4 rows affected)
1>
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