Introduction¶

What is a database?¶

definition: A database is a collection of information that exists over a long period of time.

A Database Management System (DBMS) a complex system for managing database interactions.

1. Allows users to easily create new databases and specify schema.
2. Enables users for search and modify data.
3. Stores data intelligently,
   • Protects from accidental use
   • Allows efficient access, e.g., indexing
4. Manages cuncurrent data accesses and modifications.
5. Recovers from failures and crashes.

Relational Databases¶

A database system should present the user with a view of the data organized as tables (or relations).

So Relations are represented as Tables, column headers are attribute names. Each row is a tuple.

Access with Structured Query Language (SQL).

e.g.¶

Given the database

1. What’s the balance of account “67890”?

SELECT balance
FROM Accounts
WHERE accountNo = 67890;

1. Which are the savings accounts with negative balances?

SELECT accountNo
FROM Accounts
WHERE type = ‘savings’ AND balance < 0;