创建表时计算布尔值列 [英] Computed boolean column while creating table

问题描述

我正在尝试使用计算的布尔值创建表

I'm trying to create table with computed boolean values

CREATE TABLE parts
(
    Id SERIAL PRIMARY KEY,
    Weight INTEGER NOT NULL CHECK(Weight > 0),
    Color VARCHAR(10),
    Price INTEGER NOT NULL CHECK(Price > 0),
    IsCheap BOOL AS (CASE WHEN Price <= 1000 THEN True ELSE False END),
    Name VARCHAR(30)
);

但是遇到此错误

ERROR:  syntax error at or near "AS"
LINE 7:  IsCheap BOOL AS (CASE WHEN Price <= 1000 THEN True ELSE Fal...

我也尝试使用BIT代替BOOL-同样的错误。不知道为什么它不起作用。

Also I've tried with BIT instead BOOL - same error. Have no idea why it doesn't work.

推荐答案

如果要使用计算列，则需要Postgres 12（于2019-10-03发布）。

You need Postgres 12 (released 2019-10-03) if you want to use computed columns.

和 as 本身是不够的，语法要求使用始终以... 生成的 手册中所述：

And as on its own is not enough. The syntax requires to use generated always as ... as documented in the manual:

create table parts
(
  id       serial primary key,
  weight   integer not null check (weight > 0),
  color    varchar(10),
  price    integer not null check (price > 0),
  is_cheap boolean generated always as (price <= 1000) stored,
  name     varchar(30)
);

---

如果您未使用Postgres 12，则我建议创建一个仅包含 price< = 1000 as_cheap 的视图，因为该属性的计算确实很便宜，因此不需要存储它。

---

If you are not using Postgres 12, then I would recommend to create a view that simply includes price <= 1000 as is_cheap as the calculation of that attribute is really cheap and there is no need to store it.

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