Oracle trunc function support by ClickHouse dialect

[sleshJdev]

sqlglot==25.28.0:

parse_one("SELECT trunc(current_timestamp) FROM T", dialect='oracle').sql('clickhouse')
"SELECT DATE_TRUNC('DD', CURRENT_TIMESTAMP()) FROM T"

Expected result SELECT DATE_TRUNC('day', CURRENT_TIMESTAMP()) FROM T

Here is the list of units supported by https://clickhouse.com/docs/en/sql-reference/functions/date-time-functions#date_trunc

Oracle's trunc function documentation https://docs.oracle.com/en/database/oracle/oracle-database/19/sqlrf/TRUNC-date.html

[georgesittas]

We looked into this one, but it's a bit tricky to transpile at the moment because units are not normalized like time formats. I'll close the ticket as out of scope for now, but may revisit when someone in the core team has more bandwidth. We'll also be happy to accept well-tested PRs.