WHERE clause in the subquery's SELECT statement links the inner query to the outer query : Correlated subquery « Subquery « SQL Server / T-SQL






WHERE clause in the subquery's SELECT statement links the inner query to the outer query


1> create table employee(
2>     ID          int,
3>     name        nvarchar (10),
4>     salary      int )
5> GO
1>
2> create table job(
3>     ID              int,
4>     title nvarchar  (10),
5>     averageSalary   int)
6> GO
1>
2>
3> insert into employee (ID, name, salary) values (1,  'Jason', 1234)
4> GO

(1 rows affected)
1> insert into employee (ID, name, salary) values (2,  'Robert', 4321)
2> GO

(1 rows affected)
1> insert into employee (ID, name, salary) values (3,  'Celia', 5432)
2> GO

(1 rows affected)
1> insert into employee (ID, name, salary) values (4,  'Linda', 3456)
2> GO

(1 rows affected)
1> insert into employee (ID, name, salary) values (5,  'David', 7654)
2> GO

(1 rows affected)
1> insert into employee (ID, name, salary) values (6,  'James', 4567)
2> GO

(1 rows affected)
1> insert into employee (ID, name, salary) values (7,  'Alison', 8744)
2> GO

(1 rows affected)
1> insert into employee (ID, name, salary) values (8,  'Chris', 9875)
2> GO

(1 rows affected)
1> insert into employee (ID, name, salary) values (9,  'Mary', 2345)
2> GO

(1 rows affected)
1>
2> insert into job(ID, title, averageSalary) values(1,'Developer',3000)
3> GO

(1 rows affected)
1> insert into job(ID, title, averageSalary) values(2,'Tester', 4000)
2> GO

(1 rows affected)
1> insert into job(ID, title, averageSalary) values(3,'Designer', 5000)
2> GO

(1 rows affected)
1> insert into job(ID, title, averageSalary) values(4,'Programmer', 6000)
2> GO

(1 rows affected)
1>
2>
3> select * from employee;
4> GO
ID          name       salary
----------- ---------- -----------
          1 Jason             1234
          2 Robert            4321
          3 Celia             5432
          4 Linda             3456
          5 David             7654
          6 James             4567
          7 Alison            8744
          8 Chris             9875
          9 Mary              2345

(9 rows affected)
1> select * from job;
2> GO
ID          title      averageSalary
----------- ---------- -------------
          1 Developer           3000
          2 Tester              4000
          3 Designer            5000
          4 Programmer          6000

(4 rows affected)
1>
2>
3> -- The WHERE clause in the subquery's SELECT statement links the inner query to the outer query.
4> -- This makes the inner query a correlated subquery
5>
6> SELECT TOP 29 e.ID, e.name, (SELECT j.title FROM job j WHERE j.ID = e.ID) 'title'
7> FROM Employee e
8> GO
ID          name       title
----------- ---------- ----------
          1 Jason      Developer
          2 Robert     Tester
          3 Celia      Designer
          4 Linda      Programmer
          5 David      NULL
          6 James      NULL
          7 Alison     NULL
          8 Chris      NULL
          9 Mary       NULL

(9 rows affected)
1>
2> drop table employee;
3> drop table job;
4> GO
1>
           
       








Related examples in the same category

1.Correlated subquery using the department table in both inner and outer queries
2.Correlated subquery: the inner query depends on the outer query for any of its values
3.Correlated subquery using Distinct
4.Leaf-Level Employees (Employees with No Subordinates), Correlated Subquery Syntax
5.Leaf-Level Employees (Employees with No Subordinates), Join Syntax