feat(binder): egg binder for drop statement

[eliasyaoyc]

#707

[wangrunji0408]

Rest LGTM. Thanks!

[skyzh]

Indeed I'm wondering why we're commenting out the original drop and add a new BoundDrop between the expressions. Please hold this PR a little while and I will refactor tonight.

[wangrunji0408]

Indeed I'm wondering why we're commenting out the original drop and add a new BoundDrop between the expressions. Please hold this PR a little while and I will refactor tonight.

I thought both ways are acceptable. Given that the drop statement is unlikely to be rewritten by rules, representing it as a single BoundDrop value can avoid parsing it back from the Expr in the executor. 🤔

[skyzh]

LGTM. Some futures plans in my mind:

• Why insert / create / drop are part of pub enum Expr? 🤣 Seems a little bit weird but I'm thinking if it is possible to make it more clear.
• I believe we only need to support Drop(Id) in RisingLight. We can remove cascade / remove_if_exist later.

[wangrunji0408]

Why insert / create / drop are part of pub enum Expr? 🤣 Seems a little bit weird but I'm thinking if it is possible to make it more clear.

Yeah, putting them all into the Expr is just for making a single AST representation in the planner, although these statements won't benefit much from the egg's features since there is no need to rewrite or analyze them.