将 2 个不相关的表连接在一起

Question

I have just delved into PostgreSQL and am currently trying to practice an unorthodox query whereby I want to join 2 unrelated tables, each with the same number of rows, together such that every row carries the combined columns of both tables.

These are what I have:

technical table

 position | height | technical_id
----------+--------+-------------
 Striker  |   172  |  3
 CAM      |   165  |  4
(2 rows)

footballers table

   name   | age |  country  | game_id
----------+-----+-----------+--------
 Pele     |  77 | Brazil    |  1
 Maradona |  65 | Argentina |  2
(2 rows)

What i have tried:

SELECT name, '' AS position, null AS height, age, country, game_id, null as technical_id 
from footballers 
UNION 
SELECT '' as name, position, height, null AS age,'' AS country, null as game_id, technical_id 
from technical;

Output:

   name   | position | height | age |  country  | game_id | technical_id
----------+----------+--------+-----+-----------+---------+-------------
          | Striker  |    172 |     |           |         |     3
          | CAM      |    165 |     |           |         |     4
 Maradona |          |        |  65 | Argentina |    2    |
 Pele     |          |        |  77 | Brazil    |    1    |
(4 rows)

What I'm looking for (ideally):

   name   | position | height | age |  country  | game_id | technical_id
----------+----------+--------+-----+-----------+---------+-------------
 Pele     | Striker  |   172  |  77 | Brazil    |    1    |     3
 Maradona | CAM      |   165  |  65 | Argentina |    2    |     4
(2 rows)

Answer 1

Please use below query. But its not the right way of designing the schema. You should have a foreign key.

select t1.position,t1.height,t1.technical_id,t2.name,t2.age,t2.country,t2.game_id
from
(select position,height,technical_id, row_number() over(partition by 
position,height,technical_id) as rnk) t1
inner join 
(select name,age,country,game_id, row_number() over(partition by 
name,age,country,game_id) as rnk) t2
on t1.rnk = t2.rnk;

Answer 2

You don't have a column to join on, so you can generate one. What works is a sequential number generated by row_number() . So:

select *
from (select t.*, row_number() over () as sequm
      from technical t
     ) t join
     (select f.*, row_number() over () as sequm
      from footballers f
     ) f
     using (seqnum);

Note: Postgres has extended the syntax of row_number() so it does not require an order by clause. The ordering of the rows is arbitrary and might change on different runs of the query.