How to join multiple columns in one table to another lookup table? - sql

Question

I am unable to figure out how to join a couple of tables together when multiple columns in one table refer to another table.
For example, I have a "document_statuses" table:
document_statuses table:
+-----------+-------------+
| status_id | status_name |
+-----------+-------------+
| 1 | RECEIVED |
| 2 | MISSING |
| 3 | NOT_NEEDED |
+-----------+-------------+
Now in another table, I am tracking the status of multiple documents:
filings table:
+-----------+-------------+----------------+----------------+----------------+
| filing_id | filing_name | doc1_status_id | doc2_status_id | doc3_status_id |
+-----------+-------------+----------------+----------------+----------------+
| 1 | John | 1 | 3 | 2 |
| 2 | Mikaela | 2 | 3 | 2 |
| 3 | Sam | 1 | 2 | 1 |
+-----------+-------------+----------------+----------------+----------------+
How would I write a query that pulls the status_name in for each column and produce the following result:
+-------------+-------------+-------------+------------+
| Filing Name | Doc1 Status | Doc2 Status | Doc3Status |
+-------------+-------------+-------------+------------+
| John | RECEIVED | NOT_NEEDED | MISSING |
| Mikaela | MISSING | NOT_NEEDED | MISSING |
| Sam | RECEIVED | MISSING | RECEIVED |
+-------------+-------------+-------------+------------+
I'm aware of how to do this when looking up a single field from document_statuses per row, but not multiple. If I only had one column in documents that referred to document_statuses, I'd do a simple JOIN:
SELECT filing_name, status_name
FROM documents d
LEFT JOIN document_statuses ds ON d.doc1_status = ds.status_id
But how do I do that when I need more than one?

Answer 1

You will need to join the statuses table multiple times and then alias the columns in the select clause to be formatted to be what you want. Please note that you have to alias the tables in the join clause so that you can reference the columns in the select clause of the statement.
SELECT filing_name
, ds1.status_name AS 'Doc1 Status'
, ds2.status_name AS 'Doc2 Status'
, ds3.status_name AS 'Doc3 Status'
FROM documents d
LEFT JOIN document_statuses ds1 ON d.doc1_status = ds1.status_id
LEFT JOIN document_statuses ds2 ON d.doc2_status = ds2.status_id
LEFT JOIN document_statuses ds3 ON d.doc3_status = ds3.status_id

Answer 2

You'll need to do three times joins with same table using different aliases for table.
SELECT filing_name, ds.status_name, ds1.status_name,
ds2.status_name FROM documents d
LEFT JOIN document_statuses ds ON d.doc1_status
LEFT JOIN document_statuses ds1 ON d.doc1_status
LEFT JOIN document_statuses ds2 ON d.doc1_status

Answer 3

You can do this:
select t1.filing_name, t2.status_name as doc1_status, t3.status_name as doc2_status, t4.status_name as doc3_status
from filings_table t1
inner join statuses_table t2 on t1.doc1_status_id = t2.status_id
inner join statuses_table t3 on t1.doc2_status_id = t3.status_id
inner join statuses_table t4 on t1.doc3_status_id = t4.status_id