From: "Victor \"Zverok\" Shepelev" <vshepelev@...>
Date: 2006-12-06T06:58:49+09:00
Subject: Lisp comprehensions => SQL

Hi all.

Random idea, just for fun - using "list comprehensions" for SQL queries
generation.

employees = Table.new(:id, :name, :sec_name, :salary, :age)

employees.select{|e| e.name == 'John' && e.salary > 50}.sort_by{|e|
e.age}[2,10]

#generates "select * from Employees where name = 'John' and salary > 50
order by age limit 2,10"

employees.select{|e| e.salary < 150}.count

#generates "select count(*) from Employees where salary < 150

Something like this. (I still don't know, how to limit selected columns in
obvious way)

And even more complex:

employees = Table.new(:id, :name, :sec_name, :salary, :age)
positions = Table.new(:id, :employee_id, :position_name)

(employees + positions).select{|e, p| e.id == p.employee_id}

#generates "select * from Employees, Positions where Employees.id ==
Positions.employee_id"

Idea is completely stolen from Phil Wadler's Links[1] language.
Also MS's LINQ and ruby's Mongoose DB seems to do something like this.

But the realization of above seems to be interesting task (for RubyQuiz, may
be?)

Thanks for your patience. And sorry me my English.

V.

1. http://groups.inf.ed.ac.uk/links/
2. http://en.wikipedia.org/wiki/Language_Integrated_Query
3. http://rubyforge.org/projects/mongoose/