Feature Request: Updating can get the updated value

[Kean9527]

Feature Description

In many cases, we want to get the updated value about a column, mysql can use sql like this:
UPDATE account.t_user_bill SET diamonds = @value := diamonds + ? WHERE uid = ?
But now vitess just don't support this, Can we plan to it?

Use Case(s)

updating a column and get the updated value

[frouioui]

@GuptaManan100 is that something that we plan on supporting in the SQL parser?

[GuptaManan100]

@Kean9527 @frouioui We don't support this currently, but we would like to. I'll add this to the issue tracking parsing support.

[AllMight2099]

Hey there!
I'd like to pick this issue up

[GuptaManan100]

@AllMight2099 sure, go right ahead.

[GuptaManan100]

Parsing support was added in #13032, but that itself isn't enough to support the query. The planner currently rejects this expression explicitly.