改变postgres中不工作的列类型

Question

我有一个列的类型对象，我需要使它从另一个对象类型，(表是空的)

i tried to do:

ALTER TABLE invoice_history ALTER COLUMN invoice_info TYPE invoice USING (trim(invoice_info)::invoice);

错误:函数pg_catalog.btrim(invoice_item)不存在…ALTER COLUMN invoice_info TYPE invoice USING (trim(invoice…))^提示:没有函数匹配给定的名称和参数类型。你可能需要添加显式类型强制转换。

:

ALTER TABLE invoice_history 
ALTER COLUMN invoice_info TYPE invoice USING (invoice_info::invoice)

给出这个错误:

错误:不能将invoice_item类型转换为invoice LINE 2:…UMN

我该怎么做?它是如何改变的?

Answer 1

如果表是空的(或者你不关心列值转换)，只使用null，例如:

alter table invoice_history 
alter invoice_info type invoice using null;