SQL Server/T-SQL/Subquery/Subquery Aggregate Functions

Use aggregate function in subquery

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> -- Get the number and the last name of the employee with the smallest employee number.
2>
3> SELECT emp_no, emp_lname FROM employee
4>        WHERE emp_no = (SELECT MIN(emp_no) FROM employee)
5> GO
emp_no      emp_lname
----------- --------------------
          1 Smith
(1 rows affected)
1>
2> drop table employee
3> GO
1>

Use aggregate function MAX in subquery

1> CREATE TABLE works_on        (emp_no       INTEGER NOT NULL,
2>                         project_no    CHAR(4) NOT NULL,
3>                         job CHAR (15) NULL,
4>                         enter_date    DATETIME NULL)
5>
6> insert into works_on values (1, "p1", "analyst", "1997.10.1")
7> insert into works_on values (1, "p3", "manager", "1999.1.1")
8> insert into works_on values (2, "p2", "clerk",   "1998.2.15")
9> insert into works_on values (2, "p2",  NULL,     "1998.6.1")
10> insert into works_on values (3, "p2",  NULL,     "1997.12.15")
11> insert into works_on values (4, "p3", "analyst", "1998.10.15")
12> insert into works_on values (5, "p1", "manager", "1998.4.15")
13> insert into works_on values (6, "p1",  NULL,     "1998.8.1")
14> insert into works_on values (7, "p2", "clerk",   "1999.2.1")
15> insert into works_on values (8, "p3", "clerk",   "1997.11.15")
16> insert into works_on values (7, "p1", "clerk",   "1998.1.4")
17> 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)
1>
2> select * from works_on
3> GO
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>
2> -- Use aggregate function MAX.
3>
4> SELECT emp_no FROM works_on WHERE enter_date =
5>        (SELECT MAX(enter_date)
6>          FROM works_on WHERE job = "manager")
7> GO
emp_no
-----------
          1
(1 rows affected)
1>
2> drop table works_on
3> GO
1>