为什么我不能将列从一个枚举转换为另一个枚举？

发布于 2025-01-20 02:57:26 字数 637 浏览 2 评论 0原文

鉴于此设置，

create type myenum_one as enum('foo', 'bar', 'baz');

create table mytable (
  myvalue myenum_one
);

alter table mytable
add constraint mycheckconstraint check (myvalue != 'bar');

insert into mytable values ('foo');

create type myenum_two as enum('foo', 'bar');

当尝试更改列类型时，它会失败

alter table mytable
alter column myvalue type myenum_two using myvalue::text::myenum_two;

并出现错误

错误：运算符不存在：enum_two <>枚举_one
提示：没有运算符与给定名称和参数类型匹配。您可能需要添加显式类型转换。

原文

Given this setup

create type myenum_one as enum('foo', 'bar', 'baz');

create table mytable (
  myvalue myenum_one
);

alter table mytable
add constraint mycheckconstraint check (myvalue != 'bar');

insert into mytable values ('foo');

create type myenum_two as enum('foo', 'bar');

It then fails on when trying to alter the column type

alter table mytable
alter column myvalue type myenum_two using myvalue::text::myenum_two;

With error

ERROR: operator does not exist: enum_two <> enum_one
HINT: No operator matches the given name and argument types. You might need to add explicit type casts.

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生来就爱笑 2025-01-27 02:57:26

您需要在更改列类型之前删除支票约束，然后在此之后重新创建（如果仍然相关），例如

alter table mytable
drop constraint mycheckconstraint;

alter table mytable
alter column myvalue type myenum_two using myvalue::text::myenum_two;

alter table mytable
add constraint mycheckconstraint check (myvalue != 'bar');

You need to drop the check constraint before altering the column type, and the recreate it after (if it's still relevant), like so

alter table mytable
drop constraint mycheckconstraint;

alter table mytable
alter column myvalue type myenum_two using myvalue::text::myenum_two;

alter table mytable
add constraint mycheckconstraint check (myvalue != 'bar');

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