Cassandra 更改列类型:哪些类型兼容? [英] Cassandra alter column type: which types are compatible?

问题描述

网上有一些关于列类型无法更改的示例的零散信息.例如，在 DataStax 站点 有一个提及:

• 更改聚类列的类型.
• 更改列定义了一个索引.

或者，例如，这里提到不能转换uuid 到 timeuuid.并且根据我的个人经验，我无法将 text 更改为 timestamp(我们将日期以 ISO8601 格式存储为文本，这是项目时间线早期的一个不幸决定).>

但是，我找不到关于哪些类型可以转换为哪些类型，或者至少哪些类型不能转换为哪些类型的完整描述.有人知道吗?

解决方案

好问题！我不得不承认，我也对缺乏有关此文档的详尽文档感到有些惊讶.您的问题启发我进行了一些调查，并且还博客.

从本质上讲，这里是与 Cassandra 兼容的 CQL 类型的完整列表(使用 Cassandra 2.2.0):

• ascii -> blob、文本、varchar
• bigint -> blob、时间戳、varint
• int -> blob、varint
• text -> blob、varchar
• 时间戳 -> bigint、blob、varint
• timeuuid -> blob，UUID
• varchar -> blob、文本

注意事项:

• blob 很多，因为任何东西都可以转换为 blob.
• cqlsh 允许您将 varint 转换为新的日期类型，但这是一个错误 (CASSANDRA-10027).不要真的尝试这样做.

There's some patchy information on the interwebs about some examples when column type can't be changed. For example, on the DataStax site there's a mention:

• Changing the type of a clustering column.
• Changing columns on which an index is defined.

Or, for example, here is mentioned that you can't convert uuid to timeuuid. And from my personal experience, I can't change text to timestamp (we store dates in ISO8601 format as text, an unfortunate decision early in the project timeline).

However, I can't find a full description of which types can be converted to which, or at least which types can't be converted to which. Does anyone know?

解决方案

Great question! I have to admit that I was a bit surprised at the lack of thorough documentation on this one, as well. Your question inspired me to do a little investigation and blog about it as well.

Essentially, here is a comprehensive list of Cassandra compatible CQL types (using Cassandra 2.2.0):

• ascii -> blob, text, varchar
• bigint -> blob, timestamp, varint
• int -> blob, varint
• text -> blob, varchar
• timestamp -> bigint, blob, varint
• timeuuid -> blob, UUID
• varchar -> blob, text

Notes:

• blob is in there a lot, because anything can be converted to a blob.
• cqlsh allows you to convert a varint to the new date type, but this is a bug (CASSANDRA-10027). Don't actually try that.

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