Merge multiple "is exists" queries into one statement I'm trying to figure out how to check if multiple rows exist in multiple tables in one statement.

Given the following tables:

table table_one 
========
 id
 'a'
 'b'
 'c'

table table_two
========
  id
 'aa'
 'bb'
 'cc'


This works,

SELECT 1 from table_one where id = 'a'


and

SELECT 1 from table_two where id = 'aa' 


works

How can I combine them into one statement?

I tried

 SELECT 1 FROM table_one WHERE id = 'a'
 UNION 
 SELECT 1 FROM  table_two WHERE id = 'aa'


but this just merges the results into one column so I cant tell if a particular table was missing a row.

What i'd like is a result row something this

  table_one  table_two  table_three    table_four
  =========  =========  ===========    ==========
  1          1          [null]         1
UNION removes duplicate rows from the overall result, UNION ALL will preserve them. 

To know from which table the result came, add a constant value:

SELECT 'one' as source, 
       1 
FROM table_one 
WHERE id = 'a'
UNION ALL
SELECT 'two',
       1 
FROM table_two 
WHERE id = 'aa'