Joining 3 Tables in One Select Statement - sql

Question

I have this data set with patient information/charges (Table 1).
I am looking to achieve Table 3. Table 3 shown below has:
Distinct Patient Number (Patno)
The sum of Billed Charges for each Patno (sum billed charges then group by patno)
DRG Rate from Table 2. This is just matching the DRG in Table 1 to Table 2 and getting the DRG Rate Associated with it.
Stop loss column. If the sum of Billed Charges for a patient (found in column 2) is >275000 then (SUM of Billed Charges -275000)*.195+ DRG Rate from column 3
Claim total: If there is a stop loss, then the claim total is just = to the stop loss value found in column 4. ELSE, it is equal to the DRG rate.
Note, each patient has only ONE claim, but can have multiple line items as shown in table 1.
Table 1: Raw Data
Table 2: DRG Lookup Table
Table 3: Result Table
Please let me know if you need any additional info. I know this is a lot to ask, honestly any tips/tricks advice will really help ! Thanks in advance !

Answer 1

You can try with this
SELECT PATNO, SUM([Billed Charges]) as BilledCharges,
DR.[DRG Rate],
CASE WHEN SUM([Billed Charges]) >275000 THEN ((SUM([Billed Charges])-275000 )*.195)+DR.[DRG Rate] ELSE 'NO' END AS StopLoss,
CASE WHEN SUM([Billed Charges]) >275000 THEN ((SUM([Billed Charges])-275000 )*.195)+DR.[DRG Rate] ELSE DR.[DRG Rate] END AS ClaimTotal
FROM raw_data AS RD
INNER JOIN DRG_Lookup_Table AS DR ON RD.DRG=DR.[DRG Code]
GROUP BY PATNO

Answer 2

I'm not so sure I understand the cardinality of the records in the two tables well, but this should be fine:
SELECT
t1.PATNO,
t1.[Billed Charges] AS BilledCharges,
t2.[DRG Rate],
t1.DRG,
CASE
WHEN t1.[Billed Charges] >= 275000
THEN (t1.[Billed Charges] - 275000)*.195 + t1.DRG
ELSE 0
END AS [Stop Loss],
CASE
WHEN t1.[Billed Charges] >= 275000
THEN (t1.[Billed Charges] - 275000)*.195 + t1.DRG
ELSE t2.[DRG Rate]
END AS [Claim Total]
FROM
(
SELECT PATNO, DRG, SUM([Billed Charges]) AS [Billed Charges]
FROM TABLE_1
GROUP BY PATNO, DRG
) t1
LEFT JOIN TABLE_2 t2 ON t1.DRG = t2.[DRG Code]

Answer 3

Since I couldn't recreate the tables I have not been able to check the code. Please try and let me know.
select patno,sum(billedcharges)billedcharges,(select drg_rate
from DRG_looking_table where drg_code=r.drg)DRG_Rate, drg,
(case when sum(billedcharges)>275000 then (sum(billedcharges)-275000)*.195+drg_rate else 'No' end) stop_loss,
(case when sum(billedcharges)>275000 then (sum(billedcharges)-275000)*.195+drg_rate else drg_rate end)Claim_Total
from raw_data GROUP BY PATNO