Implement CREATE/DROP INDEX

[waynexia]

What type of enhancement is this?

User experience

What does the enhancement do?

Currently, the public user interface to create/drop index is ALTER TABLE. This might work but we can also provide a more conventional way to do this like CREATE INDEX in PostgreSQL.

We don't need to keep exactly the same with PG's grammar, as there are many different concepts among us. We can discuss the detailed preferred grammar in this thread before starting implement it.

Implementation challenges

No response