Question

I have 2 tables with similar, but different data. Both tables have an insert timestamp column of their own.

Table A                      Table B
+------------+----------+    +------------+----------+
| a_created  | a_data   |    | b_created  | b_data   |
+------------+----------+    +------------+----------+
| 2012-09-01 | A        |    | 2012-09-03 | C        |
| 2012-09-05 | B        |    | 2012-09-04 | D        |
+------------+----------+    +------------+----------+

I’d like to get all the data from these tables, sorted via a merged date column by the two creation dates. I.e. I want the following results

+------------+----------+----------+
| x_created  | a_data   | b_data   |
+------------+----------+----------+
| 2012-09-01 | A        | NULL     |
| 2012-09-03 | NULL     | C        |
| 2012-09-04 | NULL     | D        |
| 2012-09-05 | B        | NULL     |
+------------+----------+----------+

Is this even possible without altering the schema? If so, how?

Answer 1

Building on mrmryb’s answer by adding the sort you asked for and using true NULLs:

select a_created as x_created,a_data,NULL as b_data 
from table_a
union all 
select b_created as x_created,NULL as a_data,b_data 
from table_b
order by 1