Clarify and standardize naming of 'schema' vs 'database'

[Benjaminhu]

The term "schema" appears in several places in the code, but in MySQL, schema is synonymous with database: https://dev.mysql.com/doc/refman/8.4/en/glossary.html#glos_schema

In MySQL, physically, a schema is synonymous with a database.

However, in other database systems like Oracle or PostgreSQL, schemas refer to groups of tables within a database. As a result, variables like "schemas" actually contain databases, which can be misleading and confusing in a broader context.

I'm happy to help clean up the naming if the change can be included in a released version.

Thank you.