在 presto 中优化窗口查询

Posted 2023-04-18

【中文标题】在 presto 中优化窗口查询

【英文标题】：Optimizing windowing query in presto

【发布时间】：2021-05-26 11:46:18

【问题描述】：

我有一个表，其中包含 user_id、col1、col2、col3、updated_at、is_deleted、day 等字段。

当前查询看起来像这样 -

 SELECT DISTINCT
    user_id,
    first_value(col1) ignore nulls OVER (partition BY user_id 
 ORDER BY
    updated_at DESC rows BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED following) AS col1,
    first_value(col2) ignore nulls OVER (partition BY user_id 
 ORDER BY
    updated_at DESC rows BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED following) AS col2,
    first_value(col3) ignore nulls OVER (partition BY user_id 
 ORDER BY
    updated_at DESC rows BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED following) AS col3,
    bool_or(is_deleted) ignore nulls OVER (partition BY user_id 
 ORDER BY
    updated_at DESC rows BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED following) AS is_deleted 
 FROM
    my_table
 WHERE
    day >= '2021-05-25'

基本上，我想要每个用户 ID 的每列的最新（第一个）值。由于每个值列都可以为空，因此我必须多次运行相同的窗口查询（对于每一列）。 目前，66% 的时间都花在了窗口化上。 有什么办法优化吗？

【参考方案1】：

好像你想要这个：

select * from (
  select * , row_number() over (partition by user_id ORDER BY updated_at DESC) rn 
  from my_table
  where day >= '2021-05-25'
) t 
where rn = 1

【讨论】：

它可以返回 OP 想要避免的 NULL。