Cassandra：将新列添加到表中 [英] Cassandra: Adding new column to the table

问题描述

您好，我刚刚在表my_table中添加了新列Business_sys：

Hi I just added a new column Business_sys to my table my_table:

   ALTER TABLE my_table ALTER business_sys TYPE set<text>;

但是我还是删除了该列名，因为我想更改列的类型：

But again I just droped this column name because I wanted to change the type of column:

  ALTER TABLE my_table DROP business_sys;

再次尝试添加具有不同类型的相同colmn名称时，出现错误消息

Again when I tried to add the same colmn name with different type am getting error message

"Cannnot add a collection with the name business_sys because the collection with the same name and different type has already been used in past"

我只是试图执行此命令以添加具有不同类型的新列-

I just tried to execute this command to add a new column with different type-

  ALTER TABLE my_table ADD business_sys list<text>;

我做错了什么？我是Cassandra的新手。

What did I do wrong? I am pretty new to Cassandra. Any suggestions?

推荐答案

您遇到了 CASSANDRA-6276 。问题是，当您在Cassandra中删除一列时，该列中的数据不仅会消失，而且Cassandra可能会尝试使用其新的比较器类型读取该数据。

You're running into CASSANDRA-6276. The problem is when you drop a column in Cassandra that the data in that column doesn't just disappear, and Cassandra may attempt to read that data with its new comparator type.

从链接的JIRA故障单中：

From the linked JIRA ticket:

不幸的是，我们不允许从比较器中删除组件，包括从ColumnToCollectionType中删除单个集合列。
如果我们允许的话，并且拥有该类型的预先存在的数据，C *根本不知道如何比较这些数据。

Unfortunately, we can't allow dropping a component from the comparator, including dropping individual collection columns from ColumnToCollectionType. If we do allow that, and have pre-existing data of that type, C* simply wouldn't know how to compare those...

。 ..即使我们这样做了，并且允许[用户]创建一个具有相同名称的不同集合，我们也会遇到一个不同的问题：新集合的比较器将用于比较潜在的不兼容类型。

...even if we did, and allowed [users] to create a different collection with the same name, we'd hit a different issue: the new collection's comparator would be used to compare potentially incompatible types.

JIRA建议在Cassandra 3.x中这可能不是问题，但我只是在3.0.3中尝试过，但由于相同的错误而失败。 / p>

The JIRA suggests that this may not be an issue in Cassandra 3.x, but I just tried it in 3.0.3 and it fails with the same error.

我做错了什么？我是Cassandra的新手。有任何建议吗？

What did I do wrong? I am pretty new to Cassandra. Any suggestions?

不幸的是，解决这个问题的唯一方法是为新列表使用不同的名称。

Unfortunately, the only way around this one is to use a different name for your new list.

这篇关于Cassandra：将新列添加到表中的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！