Translate complex SQL query using SET to Arel or Squeel

问题

How can I translate the given query using AREL or Squeel:

SET @start = '2013-05-14';
SET @end = '2013-11-01';
SET @days = DATEDIFF(@end, @start);
SET @UnusedDays = 0;
SELECT  @UnusedDays := DATEDIFF(end_at,@end) FROM PERIODS WHERE (@end > start_at AND @end <= end_at);
SELECT  @UnusedDays := @UnusedDays + DATEDIFF(@start, start_at) FROM PERIODS WHERE (@start >= start_at AND @start < end_at);
SELECT  @days + @UnusedDays - SUM(DATEDIFF(end_at, start_at)) AS Shortfall
FROM    PERIODS
WHERE   (@start >= start_at AND @start < end_at)
OR      (end_at < @end AND start_at > @start)
OR      (@end > start_at AND @end <= end_at);

A solution to use it as raw SQL would also be welcome as I could not get it running so far.

UPDATE: The period model and goals are described at SQL request to find if a period is fully covered

UPDATE2: If I try to use a raw sql query like:

query = %Q[
  SET @start = '2013-05-14';
  SET @end = '2013-11-01';
  SET @days = DATEDIFF(@end, @start);
  SET @UnusedDays = 0;
  SELECT  @UnusedDays := DATEDIFF(end_at,@end) FROM PERIODS WHERE (@end > start_at AND @end <= end_at);
  SELECT  @UnusedDays := @UnusedDays + DATEDIFF(@start, start_at) FROM PERIODS WHERE (@start >= start_at AND @start < end_at);
  SELECT  @days + @UnusedDays - SUM(DATEDIFF(end_at, start_at)) AS Shortfall
  FROM    PERIODS
  WHERE   (@start >= start_at AND @start < end_at)
  OR      (end_at < @end AND start_at > @start)
  OR      (@end > start_at AND @end <= end_at);
]

Period.connection.select_all(query).first.map{|k,v| v }.first == 0

I get the following error:

ActiveRecord::StatementInvalid:
       Mysql2::Error: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'SET @end = '2013-11-01';

来源：https://stackoverflow.com/questions/16715237/translate-complex-sql-query-using-set-to-arel-or-squeel

标签

sql

ruby-on-rails

arel

squeel