PostgreSQL：创建一个生成的列 [英] PostgreSQL: creating a generated column

问题描述

目标：

我的目标是创建一个名为 paymentPrice 的新列这是 receiptPrice ， platformFee ， delivererFee （

My goal is to create a new column called paymentPricewhich is the sum of receiptPrice, platformFee, delivererFee (which needs to display the sum of the current values).

通过阅读我认为使用生成列的文档将是实现此目标的最佳方法。

From reading the docs I thought using a generated column would be thebest way to achieve this.

语法：

ALTER TABLE
   "orders"
ADD
   "paymentPrice" FLOAT GENERATED ALWAYS AS (orders."receiptPrice" + orders."platformFee" + orders."delivererFee") VIRTUAL;'

错误：

我当前的语法如下错误，但我不知道自己在做什么错

My current syntax results in the following error, but I can't figure out what I'm doing wrong

error: syntax error at or near "("

推荐答案

如上所述，生成的列将可用在Postgres 12中。

As noted above in the comments - generated columns will be available in Postgres 12.

可以使用版本< 12：

It is possible to fake a generated column with a function in versions < 12:

https：/ /www.db-fiddle.com/f/21FtTGSuTXzZxoQX9CRUZf/0

CREATE TABLE orders (
    receiptPrice INT,
    platformFee INT,
    delivererFee INT
);

CREATE OR REPLACE FUNCTION paymentPrice(_order orders) 
RETURNS integer AS $$
  SELECT ( _order.receiptPrice + _order.platformFee + _order.delivererFee)
$$
STABLE
LANGUAGE SQL;

SELECT paymentPrice(orders) FROM orders;

我想如果有其他工具依赖它的话，它的用例就是我在哪里使用 https://github.com/graphile/postgraphile 这样的工具），或者是否应该使用查询不太冗长。

I guess a use case for this would be, if some other tooling depends on it (use cases for me where tools like https://github.com/graphile/postgraphile) or if the queries should be less verbose.

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