Question

I have this such query :

SELECT au_lname,der.col FROM authors INNER JOIN (SELECT t.au_id, COUNT(title_id) AS 'col'
                       FROM titleauthor t GROUP BY t.au_id) der ON authors.au_id=der.au_id

I want write this with let operator.How I can do this?

thanks

Answer 1

I see no good reason to use let here. You can just use a group join.

var query = from author in authors
            join title in titleAuthor on author.AuthorId equals title.AuthorId
            into titles
            where titles.Count() != 0
            select new { author.LastName, Count = titles.Count() };

You could use let for the count here, I suppose:

var query = from author in authors
            join title in titleAuthor on author.AuthorId equals title.AuthorId
            into titles
            let count = titles.Count()
            where count != 0
            select new { author.LastName, Count = count };

Or you could use a more direct translation of your original query:

var innerQuery = from title in titleAuthor
                 group title by title.AuthorId into titles
                 select new { AuthorId = titles.Key, Count = titles.Count() };
var query = from author in authors
            join titleCount in innerQuery
              on author.AuthorId equals titleCount.AuthorId
            select new { author.AuthorId, titleCount.Count };