Union Demo

-- In a Union, you are stacking rows together from two or more data sources. This can be particularly useful for situations where you get similar data from different source systems.
-- Run this code to understand how a UNION works.

-- Note that you may need to specify the schema before you table name. For example, my schema name is 'public', so I could have written 'public.immunizations' in the from portions of the UNION.

select  'Main EMR System' as Source
        ,imm.date
        ,imm.patient
        ,imm.encounter
        ,imm.code
        ,imm.description
from immunizations as imm
where date between '2019-01-01 00:00' and '2019-01-01 23:59'

UNION

select 'faxed EMR System' as Source
        ,imm.date
        ,imm.patient
        ,imm.encounter
        ,imm.code
        ,imm.description
from immunizations as imm
where date between '2018-12-31 00:00' and '2018-12-31 23:59'