Select corresponding records from another table, but just the last one

Question

I have 2 tables authors and authors_sales

The table authors_sales is updated each hour so is huge.

What I need is to create a ranking, for that I need to join both tables ( authors has all the author data while authors_sales has just sales numbers)

How can I create a final table with the ranking of authors ordering it by sales?

The common key is the: authorId

I tried with LEFT JOIN but I must be doing something wrong because I get all the authors_sales table, not just the last.

Any tip in the right direction much appreciated

Answer 1

If you're looking for aggregate data of the sales, you'd want to join the tables, group by the authorId. Something like...

select authors.author_id, SUM(author_sales.sale_amt) as total_sales
from authors
inner join author_sales on author_sales.author_id = authors.author_id
group by authors.author_id
order by total_sales desc

However (I couldn't distinguish from your question whether the above scenario or next is true), if you're only looking for the max value of the author_sales table (if the data in this table is already aggregated), you can join on a nested query for author_sales, such as...

select author.author_id, t.sales from authors
inner join 
  (select top 1 author_sales.author_id, 
    author_sales.sale_amt, 
    author_sales.some_identifier 
  from author_sales order by some_identifier desc) t
on t.author_id = author.author_id
order by t.sales desc

The some_identifier would be how you determine which record is the most recent for author_sales, whether it is a timestamp of when it was inserted or an incremental primary key, however it is set up. Depending on if the data in author_sales is aggregated already, one of these two should do it for you...

Answer 2

select a.*, sum(b.sales)
from authors as a
inner join authors_sales as b 
  using authorId
group by b.authorId
order by sum(b.sales) desc;


/* assuming column sales = total for each row in authors_sales */