MySQL：多个SELECT和OUTER JOIN

Question

I'm quite new with MySQL, and having trouble arranging some tables, I can't seem to find a solution anywhere...

To simplify, say I have two types of tables, a and b, the first in 3 pieces and the second in 2 pieces. So a1, a2, a3 that I want to merge with b1, b2 by the first column.

To join a1 and b1 I do :

SELECT a.column1, a.column2
FROM table_a1 AS a
LEFT OUTER JOIN table_b1 AS b ON (a.column1=b.column1)

Now how can I select from a1, a2, a3 and join with b1, b2 ?

Answer 1

It seems like the design might need some work.

But for now, you can do this:

SELECT 
  a.column1, a.column2
FROM 
  (SELECT * FROM table_a1
   UNION ALL SELECT * FROM table_a2
   UNION ALL SELECT * FROM table_a3) AS a 
LEFT OUTER JOIN 
  (SELECT * FROM table_b1
   UNION ALL SELECT * FROM table_b2) AS b
ON (a.column1 = b.column1)

Answer 2

It seems that you want something as simple as:

SELECT * FROM table_a1 a
LEFT JOIN table_b1 b ON b.column1 = a.column1

But Golez there has a totally different answer, which makes me think I've read the question wrong =/