[jira] [Created] (FLINK-22936) Support column comment in Schema and ResolvedSchema

["Jark Wu (Jira)" <ji...@apache.org>]

Jark Wu created FLINK-22936:
-------------------------------

             Summary: Support column comment in Schema and ResolvedSchema
                 Key: FLINK-22936
                 URL: https://issues.apache.org/jira/browse/FLINK-22936
             Project: Flink
          Issue Type: New Feature
          Components: Table SQL / API
            Reporter: Jark Wu
             Fix For: 1.14.0


In order to support column comment in catalog (FLINK-18958), we should first support column comment in Schema and ResolvedSchema. 

The API is up to discuss. Currently, we already have 10 methods for adding a column in {{Schema}}. If we want to support column comment for each kind of column, the number of column methods may double. It's not easy to maintain in the long term, and make the API complex. 

Another alternative is adding a new method {{comment(String)}} which will apply comment to the previous column. This is not a good builder style, but can make the building concise. 
For example, 

{code}
Schema.newBuilder()
                        .column("ts", DataTypes.TIMESTAMP(3)).comment("log timestamp")
                        .columnByExpression("proctime", "PROCTIME()").comment("processing time")
                        .watermark("ts", "ts - INTERVAL '5' SECOND")
                        .build()
{code}



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