SQL Server/T-SQL/Table Joins/Left Join

LEFT JOIN with group by and order by

1>
2> create table employee(
3>     ID          int,
4>     name        nvarchar (10),
5>     salary      int )
6> 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> insert into employee (ID, name, salary) values (2,  "Robert", 4321)
2> GO
1> insert into employee (ID, name, salary) values (3,  "Celia", 5432)
2> GO
1> insert into employee (ID, name, salary) values (4,  "Linda", 3456)
2> GO
1> insert into employee (ID, name, salary) values (5,  "David", 7654)
2> GO
1> insert into employee (ID, name, salary) values (6,  "James", 4567)
2> GO
1> insert into employee (ID, name, salary) values (7,  "Alison", 8744)
2> GO
1> insert into employee (ID, name, salary) values (8,  "Chris", 9875)
2> GO
1> insert into employee (ID, name, salary) values (9,  "Mary", 2345)
2> GO
1>
2> insert into job(ID, title, averageSalary) values(1,"Developer",3000)
3> GO
1> insert into job(ID, title, averageSalary) values(2,"Tester", 4000)
2> GO
1> insert into job(ID, title, averageSalary) values(3,"Designer", 5000)
2> GO
1> insert into job(ID, title, averageSalary) values(4,"Programmer", 6000)
2> GO
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
1> select * from job;
2> GO
ID          title      averageSalary
----------- ---------- -------------
          1 Developer           3000
          2 Tester              4000
          3 Designer            5000
          4 Programmer          6000
1>
2> SELECT count(e.id)
3> FROM Employee e LEFT JOIN job j
4> ON e.ID = j.ID
5> group by j.ID
6> ORDER BY j.ID
7> GO
-----------
          5
          1
          1
          1
          1
1>
2>
3>
4> drop table employee;
5> drop table job;
6> GO
1>
2>

Using TOP in left join

1>
2> create table employee(
3>     ID          int,
4>     name        nvarchar (10),
5>     salary      int )
6> 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> SELECT TOP 5 e.ID, e.Name , j.title
3> FROM Employee e LEFT JOIN job j
4> ON e.ID = j.ID
5> ORDER BY j.ID
6> GO
ID          Name       title
----------- ---------- ----------
          6 James      NULL
          5 David      NULL
          7 Alison     NULL
          8 Chris      NULL
          9 Mary       NULL
(5 rows affected)
1>
2> drop table employee;
3> drop table job;
4> GO
1>
2>