在 sqlalchemy 中实现窗口函数时需要帮助

Posted 2023-03-31

【中文标题】在 sqlalchemy 中实现窗口函数时需要帮助

【英文标题】：Need help in implementing a window function in sqlalchemy

【发布时间】：2021-09-24 01:01:56

【问题描述】：

我正在尝试实现这个窗口功能：

它按portfolio_id 分组。 在每个组中，找到最新版本。 返回每组中最新版本的记录。

我尝试在 SQLAlchemy 中这样实现它：

 subquery = session.query(
        MyTable,
        func.row_number().over(
          partition_by=MyTable.portfolio_id,
          order_by=MyTable.version.desc()).label("row_number")
      ).subquery()
      LOG.info("subquery is ".format(subquery))

      current_config = session.query(subquery).filter(subquery.c.row_number <= 1)

但是日志显示查询的是这个：

SELECT anon_1.id AS anon_1_id,
    anon_1.portfolio_id AS anon_1_portfolio_id,
    anon_1.portfolio_name AS anon_1_portfolio_name,
    anon_1.version AS anon_1_version,
    anon_1.created_at AS anon_1_created_at,
    anon_1.last_updated_at AS anon_1_last_updated_at,
    anon_1.last_updated_by AS anon_1_last_updated_by,
    anon_1.config AS anon_1_config,
    anon_1.row_number AS anon_1_row_number
FROM (
    SELECT config_table_development.id AS id,
        config_table_development.portfolio_id AS portfolio_id,
        config_table_development.portfolio_name AS portfolio_name,
        config_table_development.version AS version,
        config_table_development.created_at AS created_at,
        config_table_development.last_updated_at AS last_updated_at,
        config_table_development.last_updated_by AS last_updated_by,
        config_table_development.config AS config,
        row_number() OVER (
            PARTITION BY config_table_development.portfolio_id ORDER BY config_table_development.version DESC
            ) AS row_number
    FROM config_table_development
    ) AS anon_1
WHERE anon_1.row_number <= ?

我们绝对不会期待WHERE anon_1.row_number <= ?，我们应该期待WHERE anon_1.row_number <= 1。我该如何解决？

【参考方案1】：

问题中的SQL语句是参数化版本的语句和

WHERE anon_1.row_number <= ?

显示 where 子句及其参数占位符。问题没有显示的是参数 value 将立即出现在日志中：

2022-03-14 18:15:26,664 INFO … SELECT anon_1.id AS anon_1_id, …
WHERE anon_1.row_number <= ?
2022-03-14 18:15:26,665 INFO … [generated in 0.00033s] (1,)

这就是1 的来源。