Question

I’m trying to join two tables with the same structure if they match the primary key of a third table. Then I want to sort based on a column from the 3rd table.

Example structure:

 Table 1 - id (VARCHAR) | title (VARCHAR) | expire (TIMESTAMP)

 Table 2 - id (VARCHAR) | title (VARCHAR) | expire (TIMESTAMP)

 Table 3 - id (VARCHAR) | views (VARCHAR) | expire (TIMESTAMP)

I thought this should work but it doesn’t:

 SELECT * FROM table1 as t, table3 as t3 WHERE t.id = t3.id
 UNION
 SELECT * FROM table2 as t2, table3 as t3 WHERE t2.id = t3.id
 ORDER BY table3.expire DESC

What could accomplish this?

Answer 1

Bring the sorting column from table 3 in with a JOIN, and then sort on it.

SELECT table_1.*, table_3.expire as t3_expire
  FROM table_1
  INNER JOIN table_3 on table_1.id = table_3.id
UNION ALL
SELECT table_2.*, table_3.expire
  FROM table_2
  INNER JOIN table_3 on table_2.id = table_3.id
ORDER BY t3_expire DESC;