10. MySQL Part 1: Install, Create, Insert and SELECT
10.2 Working with Databases
Database mhanje tables cha folder. Pratyek application sathi vegla database thevaycha.
CREATE DATABASE cybercourse; -- create
CREATE DATABASE IF NOT EXISTS cybercourse; -- no error if it already exists
SHOW DATABASES; -- list all
USE cybercourse; -- select it for the next commands
SELECT DATABASE(); -- which one am I using?
SHOW TABLES; -- tables inside it
-- DROP DATABASE cybercourse; -- deletes everything inside! (commented on purpose)
| Statement type | Meaning | Examples |
|---|---|---|
| DDL – Data Definition | Structure | CREATE, ALTER, DROP, TRUNCATE, RENAME |
| DML – Data Manipulation | Rows | INSERT, UPDATE, DELETE |
| DQL – Data Query | Reading | SELECT |
| DCL – Data Control | Permissions | GRANT, REVOKE |
| TCL – Transaction Control | Transactions | START TRANSACTION, COMMIT, ROLLBACK |
Why this matters for security
In SQL injection, SELECT schema_name FROM information_schema.schemata and SHOW TABLES-style queries are how an attacker maps your databases. Least privilege means the web app user can see only its own database, so even a successful injection cannot list the others.
Ravindra Bagale's Tip
Many students forget USE cybercourse; and panic at the "No database selected" error. After every new login, run USE first or check with SELECT DATABASE();. And don't forget the ; at the end in SQL – when the prompt shows ->, MySQL is waiting for your semicolon.
Ravindra Bagale's Tip – मराठी
USE cybercourse; विसरून बरेच students "No database selected" error ला घाबरतात. प्रत्येक नवीन login नंतर आधी USE करा किंवा SELECT DATABASE(); ने check करा. आणि SQL मध्ये शेवटी ; विसरू नका – prompt -> दाखवतो म्हणजे MySQL तुमच्या semicolon ची वाट बघतोय.
Ravindra Bagale's Tip – हिंदी
USE cybercourse; भूलकर बहुत से students "No database selected" error से घबरा जाते हैं. हर नए login के बाद पहले USE करो या SELECT DATABASE(); से check करो. और SQL में आख़िर में ; मत भूलना – prompt -> दिखाए तो MySQL तुम्हारे semicolon का इंतज़ार कर रहा है.
Practice task
Create databases cybercourse and testdb, list them, switch between them with USE, and drop testdb.