self join example
SELECT
e.first_name + ' ' + e.last_name employee,
m.first_name + ' ' + m.last_name manager
FROM
sales.staffs e
INNER JOIN sales.staffs m ON m.staff_id = e.manager_id
ORDER BY
manager;self join example
SELECT
e.first_name + ' ' + e.last_name employee,
m.first_name + ' ' + m.last_name manager
FROM
sales.staffs e
INNER JOIN sales.staffs m ON m.staff_id = e.manager_id
ORDER BY
manager;self join
SELECT column_name(s)
FROM table1 T1, table1 T2
WHERE condition;what is self join
Self is joining a table to itself.
-- assume employee table as 2 different table using different alias
-- as manager and worker
-- we want to join these 2 virtual manager and worker table
-- to get manager's first name and worker's first name
-- our condition is worker's manager_id match managers employee id
SELECT manager.FIRST_NAME AS MANAGER_NAME ,
worker.FIRST_NAME AS WORKER_NAME
FROM EMPLOYEES manager
INNER JOIN EMPLOYEES worker on worker.MANAGER_ID = manager.EMPLOYEE_ID
order by 1
;Self-join
select c1.Name , c2.Name As Boss
from emp1 c1
inner join emp2 c2 on c1.Boss_id = c2.IdCopyright © 2021 Codeinu
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