Question

I have two tables with the same column names, and the same composite primary key. The composite primary key of both tables is id + year. I want to always use data from table T1, and if there exists an id + year from table T2, that’s not in table T1 I want it to be returned also.

Here’s my tables

T1

id  |  year  |  cost
----+--------+-------
1   |  2012  |  1.01
2   |  2012  |  1.02
2   |  2013  |  1.03

T2

id  |  year  |  cost
----+--------+-------
1   |  2012  |  2.01
2   |  2013  |  2.02
3   |  2013  |  2.03

I want to get:

id  |  year  |  cost
----+--------+-------
1   |  2012  |  1.01
2   |  2013  |  1.02
2   |  2013  |  1.03
3   |  2013  |  2.03

This is obviously wrong, but I tried:

SELECT
  T1.id,
  T1.year,
  T1.cost
FROM employee_cost AS T1
  INNER JOIN (select
        employee_cost_historic.id,
        employee_cost_historic.year,
        employee_cost_historic.cost
          from employee_cost_historic) AS T2
    ON T1.id = T2.id
      AND T1.year = T2.year

Answer 1

You can do this with a union all:

select id, YEAR, cost
from t2
union all
select id, YEAR, cost
from t2
where not exists (select 1 from t1 where t1.id = t2.id and t1.year = t2.year)