Question

This one is braking my head . Moving old articles rating for client from old DB to new DB where the only reference between them is first word which is separated by dash in article title. I am able to pull the info I need by using SELECT but I cant figure out how to use the result to update the new table

table that needs to be updated

UPDATE 
newDB.newtable.rating
SET  newDB.newtable.rating.rating_count = oldvotes

the select that gives me the info on oldvotes

SELECT 
    oldvotes.votes AS oldvotes, old.title AS oldtitle,newtable.news_items.title as newtitle,newtable.news_items.id AS newID
FROM 
    oldDB.news_items AS old
INNER JOIN 
     oldDB.news_items.rating_count AS oldvotes 
ON 
     oldvotes.article_id = old.id
INNER JOIN 
      newDB.newtable.news_items
ON 
      newDB.newtable.news_items.title 
LIKE CONCAT
      (  '%', SUBSTRING_INDEX( old.title,  '- ', 1 ) ,  '%' ) 

any help is appreciated!

Answer 1

If I understand correctly, you have in old.title something like thisisauniquekey-september-2012, and in news_items.title the value ‘thisisauniquekey-somethingelse’.

You could select a key (a faster key than the title) and the oldvotes into a temporary table, say, oldratings, using the same query you run now:

SELECT news_items.keytobeusedonnewtable AS keyforrating, oldvotes.votes as oldvotes FROM etc.

Then you can run the update using oldratings:

UPDATE newDB.newtable.rating SET rating_value = oldvotes FROM
newDB.newtable.rating JOIN oldratings
    ON rating.keyforrating = oldvotes.keyforrating;