binder: encapsulate lower-case conversion for identifiers

[a9QrX3Lu]

According to this comment, we should encapsulate the lower-case conversion for better extensibility. However, we can not do this by modifying the Catalog, because we have other states owning the identifiers, e.g., every field in BindContext.

I think the best way to do this is to visit the AST generated by sqlparser, and convert all the names into lower-case.

[wangrunji0408]

Just convert the input string before parsing🙈

[skyzh]

Just convert the input string before parsing🙈

But this won’t retain users’ preference when creating tables. For example, they might create column V1, but will get v1 instead.

[a9QrX3Lu]

Just convert the input string before parsing🙈

But this won’t retain users’ preference when creating tables. For example, they might create column V1, but will get v1 instead.

This is exactly what Postgres does.🙈

[a9QrX3Lu]

According to this comment, we should not convert input string into lower case. So, converting all identifiers in the AST seems to be the acceptable choice.

[yyin-dev]

Conceptually, traversing the AST sounds easy and intuitive. But since the AST is implemented as enum's in sqlparser, how do you traverse enums? Manual matches?

[skyzh]

Yes, that's true 🤣 btw I just realized that Postgres parser will convert everything to lowercase, so we might follow its convention and just convert everything to lowercase.

[yyin-dev]

so we might follow its convention and just convert everything to lowercase.

Do you mean after converting names in the AST? Converting the query string into lowercase cannot handle the following correctly:

[skyzh]

Oh, you're right. I mean all identifiers (like table name, column name) are lowercase. Probably we only need to make all table / column case-insensitive in binder.