在完全外连接中获取不同的值

Question

I have two tables that have distinct ids

Table 1    Table 2    Desired Result
+----+     +----+     +--------------------+
| id |     | id |  =  | id | a     | b     |
+----+     +----+     +--------------------+
| 1  |     | 2  |     | 1  | TRUE  | FALSE |
| 2  |     | 3  |     | 2  | TRUE  | TRUE  |
| 3  |     | 4  |     | 3  | TRUE  | TRUE  |
+----+     +----+     | 4  | FALSE | TRUE  |
                      +--------------------+

and I'm querying them like this:

SELECT
  id,
  table1.id IS NOT NULL as a,
  table2.id IS NOT NULL as b,
FROM table1
FULL JOIN table2
  USING (id)

If id is unique in table1 and in table2 is it guarunteed to be unique in the resulting table? Is there a better way to get my desired result, or is the best way?

Answer 1

i would try this option

  select id
       ,max(case when a is null then 'FALSE' else 'TRUE' end) as a
       ,max(case when b is null then 'FALSE' else 'TRUE' end) as b
  from (
         select id,'TRUE' as a,null as b
           from table1
         union all
         select id,null as a,'TRUE' as b
           from table2
        )x
group by x.id