A subquery is simply a SELECT query within a SELECT query : Subqueries « Subquery « SQL Server / T-SQL






A subquery is simply a SELECT query within a SELECT query


1> create table employee(
2>     ID          int,
3>     name        nvarchar (10),
4>     salary      int,
5>     start_date  datetime,
6>     city        nvarchar (10),
7>     region      char (1))
8> GO
1>
2> insert into employee (ID, name,    salary, start_date, city,       region)
3>               values (1,  'Jason', 40420,  '02/01/94', 'New York', 'W')
4> GO

(1 rows affected)
1> insert into employee (ID, name,    salary, start_date, city,       region)
2>               values (2,  'Robert',14420,  '01/02/95', 'Vancouver','N')
3> GO

(1 rows affected)
1> insert into employee (ID, name,    salary, start_date, city,       region)
2>               values (3,  'Celia', 24020,  '12/03/96', 'Toronto',  'W')
3> GO

(1 rows affected)
1> insert into employee (ID, name,    salary, start_date, city,       region)
2>               values (4,  'Linda', 40620,  '11/04/97', 'New York', 'N')
3> GO

(1 rows affected)
1> insert into employee (ID, name,    salary, start_date, city,       region)
2>               values (5,  'David', 80026,  '10/05/98', 'Vancouver','W')
3> GO

(1 rows affected)
1> insert into employee (ID, name,    salary, start_date, city,       region)
2>               values (6,  'James', 70060,  '09/06/99', 'Toronto',  'N')
3> GO

(1 rows affected)
1> insert into employee (ID, name,    salary, start_date, city,       region)
2>               values (7,  'Alison',90620,  '08/07/00', 'New York', 'W')
3> GO

(1 rows affected)
1> insert into employee (ID, name,    salary, start_date, city,       region)
2>               values (8,  'Chris', 26020,  '07/08/01', 'Vancouver','N')
3> GO

(1 rows affected)
1> insert into employee (ID, name,    salary, start_date, city,       region)
2>               values (9,  'Mary',  60020,  '06/09/02', 'Toronto',  'W')
3> GO

(1 rows affected)
1>
2> select * from employee
3> GO
ID          name       salary      start_date              city       region
----------- ---------- ----------- ----------------------- ---------- ------
          1 Jason            40420 1994-02-01 00:00:00.000 New York   W
          2 Robert           14420 1995-01-02 00:00:00.000 Vancouver  N
          3 Celia            24020 1996-12-03 00:00:00.000 Toronto    W
          4 Linda            40620 1997-11-04 00:00:00.000 New York   N
          5 David            80026 1998-10-05 00:00:00.000 Vancouver  W
          6 James            70060 1999-09-06 00:00:00.000 Toronto    N
          7 Alison           90620 2000-08-07 00:00:00.000 New York   W
          8 Chris            26020 2001-07-08 00:00:00.000 Vancouver  N
          9 Mary             60020 2002-06-09 00:00:00.000 Toronto    W

(9 rows affected)
1>
2> -- A subquery is simply a SELECT query within a SELECT query. 
Subqueries scalar expressions.
3>
4> -- Scalar Expressions
5> SELECT City, Salary
6>        , (SELECT AVG(Salary) FROM Employee)
7>     AS AvgSalary
8> FROM Employee
9>
10>
11>
12>
13>
14> drop table employee
15> GO
City       Salary      AvgSalary
---------- ----------- -----------
New York         40420       49580
Vancouver        14420       49580
Toronto          24020       49580
New York         40620       49580
Vancouver        80026       49580
Toronto          70060       49580
New York         90620       49580
Vancouver        26020       49580
Toronto          60020       49580

(9 rows affected)
1>
           
       








Related examples in the same category

1.Subqueries and Comparison Operators
2.A subquery can be used with comparison operators
3.Return a single value from subquery