JOIN table multiple times for same columns, from different columns - sql-server

Question

I've had a search and there are many Questions out there that sound the same but are slightly not covering what I need.
I have the following setup:
Database: Job1, Table: Document
id | rev_desc_id | created_by_id | modified_by_id | checker_id | approver_id
---|-------------|---------------|----------------|------------|------------
1 | 1 | 1 | 1 | 2 | 3
"rev_desc_id" links MySoftware.dbo.Revision_Description.id
"created_by_id", "modified_by_id", "checker_id", "approver_id" link MyCompany.dbo.Person.id
Database: MyCompany, Table: Person
id | first_name | last_name
---|------------|----------
1 | Tom | DeLonge
2 | Mark | Hoppus
3 | Travis | Barker
Database: MySoftware, Table: Revision_Description
id | name
---|------------
1 | Draft
2 | For Comment
I have the following SQL:
SELECT Document.*, Revision_Description.name AS 'Rev Description', CONCAT(Person.first_name, ' ', Person.last_name) AS 'Created By'
FROM Document
INNER JOIN MySoftware.dbo.Revision_Description
ON rev_desc_id=Revision_Description.id
INNER JOIN MyCompany.dbo.Person
ON created_by_id=Person.id
This all works fine, but I'm now at the point where I need to return the other concatenated names for "modified", "checker" and "approver". I'm not sure how to give these specific column names like "AS Created By".
I also have some other columns that need joining to other tables too.
I am pretty new to database design and I'm not trying my best to name and link them all correctly, so apologies if I'm completely wrong with all this.
Any help or suggestions would be greatly appreciated.
Thank you in advance.

Answer 1

For a lookup tables I prefer to use LEFT JOIN, but you can add the Person table N times and use an alias depending on Creator, Checker, ...
SELECT
Document.*,
Revision_Description.name AS 'Rev Description',
CONCAT(C.first_name, ' ', C.last_name) AS 'Created By',
CONCAT(M.first_name, ' ', M.last_name) AS 'Modified By',
CONCAT(K.first_name, ' ', K.last_name) AS 'Checked By'
FROM Document
INNER JOIN MySoftware.dbo.Revision_Description
ON rev_desc_id=Revision_Description.id
LEFT JOIN MyCompany.dbo.Person as C
ON created_by_id=C.id
LEFT JOIN MyCompany.dbo.Person as M
ON modified_by_id=M.id
LEFT JOIN MyCompany.dbo.Person as K
ON checked_id=K.id

Answer 2

SELECT d.*, s.name 'Rev Description',
CONCAT(c.first_name, ' ', c.last_name) CreatedBy,
CONCAT(m.first_name, ' ', m.last_name) ModifiedBy,
CONCAT(k.first_name, ' ', k.last_name) CheckedBy,
CONCAT(a.first_name, ' ', a.last_name) ApprovedBy,
FROM Document d
JOIN MySoftware.dbo.Revision_Description s
ON s.id = d.rev_desc_id
left JOIN MyCompany.dbo.Person c
ON c.id = d.created_by_id
left JOIN MyCompany.dbo.Person m
ON m.id = d.modified_by_id
left JOIN MyCompany.dbo.Person k
ON k.id = d.checker_id
left JOIN MyCompany.dbo.Person a
ON a.id = d.approver_id