SQL to populate values in xml list - sql-server

Question

In an SQL Server sproc I need to generate xml using data originating from two different tables. In my example below, the patient number for type EPI comes from one table and the patient number for type MRN comes from another table. To create the xml I am using a UNION to combine the records from two distinct select statements and then using 'FOR XML PATH'. Is there a different way - such as using two select sub-queries without using UNION?
<Patients>
<Patient>
<Number>1234</Number>
<NumberType>EPI</NumberType>
</Patient>
<Patient>
<Number>5678</Number>
<NumberType>MRN</NumberType>
</Patient>
</Patients>
Thanks in advance.

Answer 1

If I understood your answer to my question, you are not really joining the tables on PatientId, you are just creating a list of all the data from both tables, and you don't need to group the records by patient.
Yes, UNION is the easiest way to accomplish a single list.
However, since you want to output xml, there is an alternate that can be done without UNION, per your question:
Assuming you have two tables that might look something like this:
CREATE TABLE SrcA (PatientId int, NumberA int, TypeA varchar(16));
CREATE TABLE SrcB (PatientId int, NumberB int, TypeB varchar(16));
with sample values like this (note how each table has one record not in the other):
INSERT INTO SrcA VALUES(100, 1234, 'EPI'), (200, 2222, 'EPI'), (400, 4444, 'EPI');
INSERT INTO SrcB VALUES(100, 5678, 'MRN'), (200, 2121, 'MRN'), (300, 3131, 'MRN');
Then the following query:
SELECT
(SELECT SA.NumberA AS Number, SA.TypeA AS NumberType WHERE SA.NumberA IS NOT NULL FOR XML PATH('Patient'), TYPE),
(SELECT SB.NumberB AS Number, SB.TypeB AS NumberType WHERE SB.NumberB IS NOT NULL FOR XML PATH('Patient'), TYPE)
FROM SrcA SA
FULL OUTER JOIN SrcB SB ON SA.PatientId = SB.PatientId
FOR XML PATH(''), ROOT('Patients')
will produce:
<Patients>
<Patient>
<Number>1234</Number>
<NumberType>EPI</NumberType>
</Patient>
<Patient>
<Number>5678</Number>
<NumberType>MRN</NumberType>
</Patient>
<Patient>
<Number>2222</Number>
<NumberType>EPI</NumberType>
</Patient>
<Patient>
<Number>2121</Number>
<NumberType>MRN</NumberType>
</Patient>
<Patient>
<Number>4444</Number>
<NumberType>EPI</NumberType>
</Patient>
<Patient>
<Number>3131</Number>
<NumberType>MRN</NumberType>
</Patient>
</Patients>