[mysql] expose update_before field in the metadata through flink sql

[EMsnap]

Is your feature request related to a problem? Please describe.

see https://nightlies.apache.org/flink/flink-docs-master/zh/docs/connectors/table/formats/canal/

in canal json user would want OLD field to know the update before data before UPDATE record

Describe the solution you'd like add update before field in meta data

Describe alternatives you've considered add update before field in meta data

[leonardBang]

Thanks @EMsnap for report this issue, I think what you want it the operation type(UPDATE_BEFORE and UPDATE_AFTER) in FLINK SQL, right? Would you like to take this issue?

[tisonkun]

@leonardBang there's already a patch https://github.com/ververica/flink-cdc-connectors/pull/1139. Is it a good fit?

[leonardBang]

@leonardBang there's already a patch #1139. Is it a good fit?

Cool, but I'm hesitate to introduce the update_before field which may lead to some correctness issue in Flink SQL operators which need retraction, how do you think the correctness tradeoff and extensibility ? @tisonkun

[PatrickRen]

Closing this issue because it was created before version 2.3.0 (2022-11-10). Please try the latest version of Flink CDC to see if the issue has been resolved. If the issue is still valid, kindly report it on Apache Jira under project Flink with component tag Flink CDC. Thank you!