SQL Exercise: List the employees who are senior to their own manager

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63. From the following table, write a SQL query to find those employees who are senior to their manager. Return complete information about the employees.

Pictorial Presentation:

Sample table: employees

Sample Solution:

SELECT *
FROM employees w,
     employees m
WHERE w.manager_id = m.emp_id
  AND w.hire_date < m.hire_date;

Sample Output:

 emp_id | emp_name | job_name | manager_id | hire_date  | salary  | commission | dep_id | emp_id | emp_name | job_name  | manager_id | hire_date  | salary  | commission | dep_id
--------+----------+----------+------------+------------+---------+------------+--------+--------+----------+-----------+------------+------------+---------+------------+--------
  66928 | BLAZE    | MANAGER  |      68319 | 1991-05-01 | 2750.00 |            |   3001 |  68319 | KAYLING  | PRESIDENT |            | 1991-11-18 | 6000.00 |            |   1001
  67832 | CLARE    | MANAGER  |      68319 | 1991-06-09 | 2550.00 |            |   1001 |  68319 | KAYLING  | PRESIDENT |            | 1991-11-18 | 6000.00 |            |   1001
  65646 | JONAS    | MANAGER  |      68319 | 1991-04-02 | 2957.00 |            |   2001 |  68319 | KAYLING  | PRESIDENT |            | 1991-11-18 | 6000.00 |            |   1001
  63679 | SANDRINE | CLERK    |      69062 | 1990-12-18 |  900.00 |            |   2001 |  69062 | FRANK    | ANALYST   |      65646 | 1991-12-03 | 3100.00 |            |   2001
  64989 | ADELYN   | SALESMAN |      66928 | 1991-02-20 | 1700.00 |     400.00 |   3001 |  66928 | BLAZE    | MANAGER   |      68319 | 1991-05-01 | 2750.00 |            |   3001
  65271 | WADE     | SALESMAN |      66928 | 1991-02-22 | 1350.00 |     600.00 |   3001 |  66928 | BLAZE    | MANAGER   |      68319 | 1991-05-01 | 2750.00 |            |   3001
(6 rows)

Explanation:

The said query in SQL that selects all columns from the 'employees' table twice, with different aliases "w" and "m" to find all employees who were hired before their manager.

The query joins the 'employees' table to itself, to create a relationship between the employee and their manager based on the emp_id and manager_id columns, and the hire date comparison then filters the results to only show employees who were hired earlier than their manager using the WHERE clause.

Relational Algebra Expression:

Relational Algebra Tree:

Practice Online

Sample Database: employee

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