Simplify multiple joins - sql-server

Question

I have a Claims table with 70 columns, 16 of which contain diagnosis codes. The codes mean nothing, so I need to pull the descriptions for each code located in a separate table.
There has to be a simpler way of pulling these code descriptions:
-- This is the claims table
FROM
[database].[schema].[claimtable] AS claim
-- [StagingDB].[schema].[Diagnosis] table where the codes located
-- [ICD10_CODE] column contains the code
LEFT JOIN
[StagingDB].[schema].[Diagnosis] AS diag1 ON claim.[ICDDiag1] = diag1.[ICD10_CODE]
LEFT JOIN
[StagingDB].[schema].[Diagnosis] AS diag2 ON claim.[ICDDiag2] = diag2.[ICD10_CODE]
LEFT JOIN
[StagingDB].[schema].[Diagnosis] AS diag3 ON claim.[ICDDiag3] = diag3.[ICD10_CODE]
-- and so on, up to ....
LEFT JOIN
[StagingDB].[schema].[Diagnosis]AS diag16 ON claim.[ICDDiag16] = diag16.[ICD10_CODE]
-- reported column will be [code_desc]
-- ie:
-- diag1.[code_desc] AS Diagnosis1
-- diag2.[code_desc] AS Diagnosis2
-- diag3.[code_desc] AS Diagnosis3
-- diag4.[code_desc] AS Diagnosis4
-- etc.

Answer 1

I think what you are doing is already correct in given scenario.
Another way can be from programming point of view or you can give try and compare ther performace.
i) Pivot Claim table on those 16 description columns.
ii) Join the Pivoted column with [StagingDB].[schema].[Diagnosis]
Another way can be to put [StagingDB].[schema].[Diagnosis] table in some #temp table
instead of touching large Staging 16 times.
But for data analysis has to be done to decide if there is any way.

Answer 2

You can go for UNPIVOT of the claimTable and then join with Diagnosis table.
TEST SETUP
create table #claimTable(ClaimId INT, Diag1 VARCHAR(10), Diag2 VARCHAR(10))
CREATE table #Diagnosis(code VARCHAR(10), code_Desc VARCHAR(255))
INSERT INTO #ClaimTable
VALUES (1, 'Fever','Cold'), (2, 'Headache','toothache');
INSERT INTO #Diagnosis
VALUEs ('Fever','Fever Desc'), ('cold','cold desc'),('headache','headache desc'),('toothache','toothache desc');
Query to Run
;WITH CTE_Claims AS
(SELECT ClaimId,DiagnosisNumeral, code
FROM #claimTable
UNPIVOT
(
code FOR DiagnosisNumeral in ([Diag1],[Diag2])
) as t
)
SELECT c.ClaimId, c.code, d.code_Desc
FROM CTE_Claims AS c
INNER JOIN #Diagnosis as d
on c.code = d.code
ResultSet
+---------+-----------+----------------+
| ClaimId | code | code_Desc |
+---------+-----------+----------------+
| 1 | Fever | Fever Desc |
| 1 | Cold | cold desc |
| 2 | Headache | headache desc |
| 2 | toothache | toothache desc |
+---------+-----------+----------------+