SQL Query Source Code

Question

I have 3 tables. One table has all the people, [Pat], each with a unique [PatId]. The second table has all the insurance company information, [Ins], each with a unique [InsId]. The third table has the patient insurance info, [PatIns]. In the [PatIns] table, some patients (also [PatId]) have secondary or 3rd insurance and it denoted in [InsType] as 1, 2, or 3. I need a SQL query that will not only join the 3 tables, but also return the data when a patient has secondary or third insurance. So far I have:

SELECT * 

FROM [XEREX_TEST].[dbo].[xrxPat], 

[XEREX_TEST].[dbo].[xrxIns],

[XEREX_TEST].[dbo].[xrxPatIns]

[XEREX_TEST].[dbo].[xrxPatIns] AS INS2,

[XEREX_TEST].[dbo].[xrxPatIns] AS INS3 

WHERE [xrxPat].[PatId]=[xrxPatIns].[PatId] 

AND [xrxPatIns].[PatId] = INS2.[PatId] 

AND [xrxPatIns].[PatId] = INS3.[PatId]

AND [xrxIns].[RecNo]=[xrxPatIns].[InsId] 

AND [xrxPatIns].[InsType]=1

AND INS2.[InsType]=2 

AND INS3.[InsType]=3;   

Problem is this only returns patients with 3 insurances. I would like to return all the patients and null values for tables INS2 and/or INS3 if the patient only has 1 insurance. Any idea how to do this?

Answer 1

While this could be done in the where clause, you're best off changing to using explicit joins, as that makes the code easier to read as well.

SELECT
  *
FROM [XEREX_TEST].[dbo].[xrxPat]
INNER JOIN [XEREX_TEST].[dbo].[xrxIns]
    ON [xrxPat].[PatId] = [xrxIns].[PatId]
INNER JOIN [XEREX_TEST].[dbo].[xrxPatIns]
    ON [xrxIns].[RecNo] = [xrxPatIns].[InsId]
    AND [xrxPatIns].[InsType] = 1
LEFT JOIN [XEREX_TEST].[dbo].[xrxPatIns] AS INS2
    ON [xrxIns].[RecNo] = INS2.[PatId]
    AND INS2.[InsType] = 2
LEFT JOIN [XEREX_TEST].[dbo].[xrxPatIns] AS INS3
    ON [xrxIns].[RecNo] = INS3.[PatId]
    AND INS3.[InsType] = 3;