Checking if database is used currently when dropping database

[killme2008]

What type of enhancement is this?

User experience

What does the enhancement do?

The GreptimeDB doesn't checking if current session is using the database which will be dropped:

mysql> create database test;
Query OK, 1 row affected (0.05 sec)

mysql> use test;
Database changed

mysql> drop database test;
Query OK, 0 rows affected (0.02 sec)

It's better to prevent dropping the database if the user is using it in MySQL or Postgres Session.

Implementation challenges

Looks like it can be checked at

greptimedb/src/operator/src/statement/ddl.rs

Line 657 in 466f7c6

pub async fn drop_database(

Retrieving the current database using QueryContext#current_schema and checking if it's the database to be dropped.

[etolbakov]

I might give it a shot if that’s ok