Hi Margaret, let's clear up your confusion step by step!

• SID: First off, in Oracle (since SID is most commonly an Oracle term), the SID identifies a database instance—not the database name (they might share the same string, but they're different things), and it's not a schema name.
• Username: Here's the critical point: In Oracle, a username is exactly the same as its corresponding schema name. When you create a user, Oracle automatically creates a schema with the same name, and all objects (tables, views, etc.) you create under that user are stored in this schema by default.
• Connection Name: This is just a custom alias you set up in your database client (like SQL Developer or PL/SQL Developer) to make it easier to remember your connection. It has no relation to the actual schema name.

If you're already connected to the database, run either of these simple SQL commands to get your current schema:

-- Method 1: Use system context
SELECT SYS_CONTEXT('USERENV', 'CURRENT_SCHEMA') FROM DUAL;

-- Method 2: Shorter version
SELECT USER FROM DUAL;

Both will return the schema you're currently working with, which should match the username you used to log in.

If you want to see all schemas (and their associated users) in the database, you can run:

-- Requires DBA privileges
SELECT username FROM dba_users;

-- If you don't have DBA access, use this to see schemas you can access
SELECT username FROM all_users;

Since you've already edited tables and objects via a previous connection, the schema you worked with is definitely tied to the username you used for that connection. For example, if you logged in as MARGARET, all your edited tables live in the MARGARET schema.

内容的提问来源于stack exchange，提问作者Maggie