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

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


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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

(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>
6SELECT TOP 29 e.ID, e.name, (SELECT j.title FROM job j WHERE j.ID = e.ID'title'
7FROM Employee e
8> GO
ID          name       title
----------- ---------- ----------
          Jason      Developer
          Robert     Tester
          Celia      Designer
          Linda      Programmer
          David      NULL
          James      NULL
          Alison     NULL
          Chris      NULL
          Mary       NULL

(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
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