Misleading error message for typo in IF NOT EXISTS about sqlparser-rs

[tisonkun]

@alamb sorry I copy the wrong code snippet. Let me update it when I return to my laptop.

[tisonkun]

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

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

[tisonkun]

Some corner case -

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

[tisonkun]

@alamb Updated.

[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