How create multiplies select with inner join in Ruby on Rails? - mysql

Question

I want create that query
SELECT * FROM `books` INNER JOIN (SELECT * FROM `authors` GROUP by `author_id`) as variable ON variable.`id` = `books`.`id` INNER JOIN `student` ON `student`.`id` = variable.`id` WHERE (`books`.`id` = '1');
For the question, of course, the request itself is slightly changed, but that's not the point. Can you please help me to make this kind of request in Ruby on Rails style
I tried, but it's a bit not what I want ... I have to do INNER JOIN (Select ... )
Book.select('*').joins(author: :student).where("`books`.`id` = '1'").group("author.author_id")

Answer 1

While your SQL does not appear to make any logical sense you can construct this query as follows:
author_table = Author.arel_table
author_sub_query = Arel::Nodes::TableAlias.new(
author_table
.project(author_table[Arel.star])
.group(author_table[:author_id]), 'variable')
author_join = Arel::Nodes::InnerJoin.new(
author_sub_query,
author_sub_query.create_on(author_sub_query[:id].eq(Book.arel_table[:id])))
student_join = Arel::Nodes::InnerJoin.new(
Student.arel_table,
author_sub_query.create_on(Student.arel_table[:id].eq(author_sub_query[:id])))
Book
.select(Arel.star)
.joins(author_join,student_join)
.where(id: 1)
Which will produce:
SELECT
*
FROM
`books`
INNER JOIN (SELECT `authors`.* FROM `authors` GROUP BY `authors`.`author_id`) `variable`
ON `variable`.`id` = `books`.`id`
INNER JOIN `students`
ON `students`.`id`= `variable`.`id`
WHERE
`books`.`id` = 1
That being said I have no idea what you are trying to do with this but if the intent is to eager load this data, you could try making these changes to the above:
author_sub_query = Arel::Nodes::TableAlias.new(
author_table
.project(author_table[Arel.star])
.group(author_table[:author_id]), Author.table_name)
Book
.joins(author_join,student_join)
.eager_load(author: :student)
.where(id: 1)