bug: When case sensitivity is enabled, some system functions cannot be used

[cdmikechen]

Search before asking

• I had searched in the issues and found no similar issues.

Version

v1.2.642-nightly

What's Wrong?

The version function cannot be used after unquoted_ident_case_sensitive is set to the global configuration.

SELECT VERSION() :

(databend_sqlalchemy.errors.Error) Code: None. APIError: ResponseError with 1008: error:
  --> SQL:1:8
  |
1 | SELECT VERSION()
  |        ^^^^^^^^^ no function matches the given name: 'VERSION', do you mean 'version', 'haversine'?
[SQL: SELECT VERSION()]
(Background on this error at: https://sqlalche.me/e/14/dbapi)

SELECT currentDatabase() :

(databend_sqlalchemy.errors.Error) Code: None. APIError: ResponseError with 1008: error:
  --> SQL:1:8
  |
1 | SELECT currentDatabase()
  |        ^^^^^^^^^^^^^^^^^ no function matches the given name: 'currentDatabase', do you mean 'currentdatabase', 'current_database', 'currentuser', 'current_user', 'current_role', 'current_timestamp'?

In my understanding, case sensitivity should only be applied to user-created table names and field names, and system functions should not need this criterion.

How to Reproduce?

SET GLOBAL unquoted_ident_case_sensitive=1;
SELECT VERSION();

Are you willing to submit PR?

• Yes I am willing to submit a PR!

[sundy-li]

 let func_name = normalize_identifier(name, self.name_resolution_ctx).to_string();
                let func_name = func_name.as_str();
                if !is_builtin_function(func_name)
                    && !Self::all_sugar_functions().contains(&func_name)

we should search by the lowercase of func_name .