Where did ClickHouse store Json sub-column schema

[dyang]

Hi I have questions about ClickHouse dynamic Json type :
1  is there any good way to find out all existing key in Json object instead of describe whole table ? this would help query don’t not include no existing column  and got errors , and also help to find out how many columns we really have in a table.
2 if some keys get delete because of TTL or some other reasons , does ClickHouse will throw key not existing error or it will still remember them in some metadata place ?

Thanks!

1.