Question

I have two tables, lets say table1 and table2 with common columns, id and update_date. I am looking to get the id’s and update_date based on latest update_date in descending order. I have used ‘union’ and ‘order by’ together which gave the results in descending order of update_date but there are duplicate id’s which I am not sure how to get rid of.

My query is like,

(select id,update_date from table1 where [condition])
UNION
(select id,update_date from table2 where [condition])
order by update_date desc;

I can just get rid of the duplicate id’s by adding select distinct id from (above query) as temp; but the problem is that I need the update_date too.

Can anyone suggest how to get rid of duplicates and still get both id and update_date information.

Answer 1

Assuming you want the latest update out of duplicates this one should work:

SELECT id, max(update_date) AS last_update
FROM
  ( (select id,update_date from table1 where [conditions])
     UNION
    (select id,update_date from table2 where [conditions]) ) both_tables
GROUP BY id
ORDER by last_update DESC