为什么我不能将列从一个枚举转换为另一个？

Question

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');

然后在尝试更改列类型时失败

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

有错误

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.

Answer 1

您需要在更改列类型之前删除检查约束，并在之后重新创建它（如果它仍然相关），就像这样

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');

为什么我不能将列从一个枚举转换为另一个？

Why can't I convert a column from one enum to another?

postgresql

enums

alter-column