获取函数复制的数据

Question

我有一个非常复杂的数据结构，它位于多个表中。我有一个函数可以复制该结构。我想像这样在单个查询中制作副本并获取新创建的数据：

SELECT
    *
FROM
    main_table
    JOIN other_table
    ON (main_table.id = other_table.main_id)
WHERE
    main_table.id = make_copy(old_id);

副本已成功创建，但未被上述查询return编辑。我想它对于外部查询还是不可见的，或者以某种方式 committed.

我也试过 WITH ... SELECT ... 但没有成功...

函数make_copy(id)声明为VOLATILE，因为它修改了数据库，同一个参数多次调用会创建多个副本。

可能的解决方案是 make_copy(id) 函数将 return 整个新数据结构 (SELECT * FROM make_copy(old_id)) 但它需要很多别名（许多表有 id 或name 列）。此外，我最终会在很多地方构建（读取）该数据结构。

如何在一个查询中调用该函数并使用其结果（以及所有副作用）？

Answer 1

如果不将其拆分为两个查询，恐怕这是不可能的。

CTE 帮不了你 - Data-Modifying Statements in WITH（请参阅更新 table 内部的示例）：

...The sub-statements in WITH are executed concurrently with each other and with the main query. Therefore, when using data-modifying statements in WITH, the order in which the specified updates actually happen is unpredictable. All the statements are executed with the same snapshot (see Chapter 13), so they cannot “see” one another's effects on the target tables. This alleviates the effects of the unpredictability of the actual order of row updates, and means that RETURNING data is the only way to communicate changes between different WITH sub-statements and the main query...

而且我猜你也不能用函数来做到这一点 - Function Volatility Categories:

For functions written in SQL or in any of the standard procedural languages, there is a second important property determined by the volatility category, namely the visibility of any data changes that have been made by the SQL command that is calling the function. A VOLATILE function will see such changes, a STABLE or IMMUTABLE function will not. ... VOLATILE functions obtain a fresh snapshot at the start of each query they execute.

获取函数复制的数据

Get data copied by a function

postgresql

transactions

function

common-table-expression