Get hierarchy of all different level of managers - sql

Question

I'm using pgAdmin4 and I have a SQL table with employee/manager HR data that looks like this:
| employee_id | email_address | full_name | band_lvl | manager_id |
| 5592 | jillr#ex.org | Jill Rhode | 20 | 6521 |
| 6421 | racheln#ex.org | Rachel Nam | 40 | 4251 |
| 2818 | todda#ex.org | Todd Alex | 25 | 6421 |
| 4251 | jalens#ex.org | Jalen Smith | 60 | 2199 |
| 6521 | tolun#ex.org | Tolu Nagoye | 30 | 2199 |
| 7831 | jina#ex.org | Ji Na | 80 | NULL |
| 2199 | zaynm#ex.org | Zayn Mate | 70 | 7831 |
Based on the first manager_id and employee_id, I'm seeking to return the following columns: Level1 Manager Name, Level1 Manager Email, Level1 Manager Band Lvl, Level1 Manager Manager's Id. I then want to do that for each manager that's a step above, until there are no higher managers.
The desired output should look like this:
| employee_id | email_address | full_name | band_lvl | manager_id | Lvl1 Mng Nm | Lvl1 Mng Email | Lvl1 Mng Band Lvl | Lvl1 Mng Mngs Id | Lvl2 Mng Nm | Lvl2 Mng Email | Lvl2 Mng Band Lvl | Lvl2 Mng Mngs Id |
| 5592 | jillr#ex.org | Jill Rhode | 20 | 6521 | Tolu Nagoye | tolun#ex.org | 30 | 2199 | Zayn Mate | zaynm#ex.org | 70 | 7831 |
| 6421 | racheln#ex.org | Rachel Nam | 40 | 4251 | Jalen Smith | jalens#ex.org | 60 | 2199 | Zayn Mate | zaynm#ex.org | 70 | 7831 |
| 2818 | todda#ex.org | Todd Alex | 25 | 6421 | Rachel Nam | racheln#ex.org | 40 | 4251 | Jalen Smith | jalens#ex.org | 60 | 2199 |
| 4251 | jalens#ex.org | Jalen Smith | 60 | 2199 | Zayn Mate | zaynm#ex.org | 70 | 7831 | Ji Na | jina#ex.org | 80 | NULL |
| 6521 | tolun#ex.org | Tolu Nagoye | 30 | 2199 | Zayn Mate | zaynm#ex.org | 70 | 7831 | Ji Na | jina#ex.org | 80 | NULL |
| 7831 | jina#ex.org | Ji Na | 80 | NULL | NULL | NULL | NULL | NULL | NULL | NULL | NULL | NULL |
| 2199 | zaynm#ex.org | Zayn Mate | 70 | 7831 | Ji Na | jina#ex.org | 80 | NULL | NULL | NULL | NULL | NULL |
So far, this is what I've come up with, to get the first columns for the Level 1 Manager; however, I don't know where to go from here, as I'm very new to SQL:
SELECT B.employee_id,
B.email_address,
B.full_name,
B.band_lvl,
B.manager_id,
B1.full_name AS L1_mng_nm,
B1.email_address AS L1_mng_email,
B1.band_lvl AS L1_mng_band_lvl,
B1.manager_id AS L1_mgr_mgrs_id
FROM hrdata B
INNER JOIN hrdata B1 ON
B.manager_id = B1.employee_id;

Answer 1

Your query is close, but you would need to make a few changes to get to your desired output. To begin, I would recommend doing a LEFT JOIN as opposed to an INNER JOIN, as the INNER JOIN will not return null values and will instead drop records that it cannot find a match for in both tables (in this case, if it cannot find a match on manager_id to employee_id from the first use of hrdata to the second use of hrdata).
After that, your query should look similar to what you have already done, just with another self-join to get the second-level manager data:
SELECT B.employee_id,
B.email_address,
B.full_name,
B.band_lvl,
B.manager_id,
B1.full_name AS L1_mng_nm,
B1.email_address AS L1_mng_email,
B1.band_lvl AS L1_mng_band_lvl,
B1.manager_id AS L1_mgr_mgrs_id,
B2.full_name AS L2_mng_nm,
B2.email_address AS L2_mng_email,
B2.band_lvl AS L2_mng_band_lvl,
B2.manager_id AS L2_mgr_mgrs_id,
FROM hrdata B
LEFT JOIN hrdata B1
ON B1.employee_id = B.manager_id
LEFT JOIN hrdata B2
ON B2.employee_id = B1.manager_id