Rails order by 在 group by 之前，如何处理了

luffycn · February 10, 2015 · Last by zlx_star replied at February 10, 2015 · 2760 hits

SELECT * FROM 

(
select * from `my_table` order by id asc
) as my_table_tmp

group by cat_id

order by id desc

这种 SQL，在 active record 中如何处理了？

hooopo #1 February 10, 2015

MyTable.find_by_sql <<-SQL
  SELECT * FROM
  (SELECT * FROM `my_table` ORDER BY  id ASC) AS my_table_tmp
  GROUP BY cat_id
  ORDER BY id DESC
SQL

billy #2 February 10, 2015

楼主说话好像有以“了”结尾的习惯，可能你是无意，但听起来是不太有礼貌。

luffycn #3 February 10, 2015

@hooopo 这种方式虽然直接，可是我还需要把结果跟其它的 scope 方法联合起来使用，跟 kamirani 分页结合起来用，会报错

zlx_star #4 February 10, 2015

order by 在 group by 之前，可以使用 calculation 函数，类似于 max 之类的

# 一个思路，未验证
select max(id) as mid from `my_table` group by cat_id order by mid desc;

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