在一行上显示来自同一个连接表的不同值

Question

There are two doctors (DOC_A and DOC_B) assigned to every patient. There are 3 tables. The PATIENT table has the Patient_ID and DOC_A's DOC_ID. The CONSULT table has Patient_ID and DOC_B's DOC_ID. Finally, the DOCTOR table has both DOC_A and DOC_B's DOC_ID with their FirstName and LastName.

I'd like to show a distinct Patient_ID on each row with both DOC_A and DOC_B with FirstName and LastName (concatenated) instead of DOC_ID's.

Example Output (manually created):

Patient_ID	DOC_A FirstLast	DOC_B FirstLast
123	John Smith	Jane Smith
456	Nathaniel Hawkeye	Cora Munroe

Answer 1

If you think about the PATIENT and CONSULT table as being 1 table (because they share a Patient_ID), it gets a little easier to imagine the joins to the DOCTOR table... you have to join twice which is fine as long as you use an alias:

select p.patient_id
     , concat(doca.firstname,' ',doca.lastname) as DOC_A_FirstLast
     , concat(docb.firstname,' ',docb.lastname) as DOC_B_FirstLast
  from dbo.PATIENT p
  join dbo.CONSULT c
    on c.patient_id = p.patient_id
  join dbo.DOCTOR doca
    on doca.doc_id = p.doc_id
  join dbo.DOCTOR docb
    on docb.doc_id = c.doc_id;