不支持add column if not exists语法，解析会报错

[squestc]

Please provide a detailed title (e.g. "Broker crashes when using TopN query with Bound filter" instead of just "Broker crashes").

Affected Version

1.2.23
The Druid version where the problem was encountered.

Description

解析sql的时，如果有add column if not exists语法会报错，但是sql是可以执行成功的
Please include as much detailed information about the problem as possible.

• Cluster size
• Configurations in use
• Steps to reproduce the problem
• The error message or stack traces encountered. Providing more context, such as nearby log messages or even entire logs, can be helpful.
• Any debugging that you have already done

[asdf2014]

Please report this to https://github.com/alibaba/druid