Misleading error message for typo in IF NOT EXISTS

[tisonkun]

See also GreptimeTeam/greptimedb#3471.

For sqlparser-rs -

fn main() {
    let sql = "CREATE TABLE IF NOT EXIST ();";

    let dialect = GenericDialect {};

    let ast = Parser::parse_sql(&dialect, sql).unwrap();

    println!("AST: {ast:?}");
}

throws:

called `Result::unwrap()` on an `Err` value: ParserError("Expected end of statement, found: NOT at Line: 1, Column 17")

IIUC if we found IF already, the next keywords SHOULD BE NOT EXIST and thus the parsing logics should be .expect_keywords.

[tisonkun]

Some corner case -

• IF as the table name can be legal.
• What CREATE TABLE NOT EXISTS ... should report?

[alamb]

👍 makes sense to me -- a nicer error message would indeed be good

[tisonkun]

@alamb the challenging part is described in #1169 (comment). Even if we look ahead IF, we cannot simply expect_keywords because it can be a table identifier.

Keep a backtrace would be the way but it seems too complex for me to working out now ...

[alamb]

You could potentially special case the error message, perhaps

[tisonkun]

I made an attempt at GreptimeDB - GreptimeTeam/greptimedb#3817

If things go well, I'll try to make similar changes to sqlparser-rs.