Relational Databases Lecture 2

Questions and Answers

What is a database?

A database is a collection of information that is stored and organized for easy access, management, and updating.

Which of the following are primary keys? (Select all that apply)

Supplier

SupplierID (correct)

Phone

ItemID (correct)

There can be multiple primary keys in a table.

False

Foreign keys can only contain values present in the parent table’s primary key column.

True Signup and view all the answers

What does SQL stand for?

Structured Query Language Signup and view all the answers

What is the purpose of the Data Definition Language (DDL)?

To build and modify the structure of tables Signup and view all the answers

A ________ diagram is a graphical representation of an information system that shows the relationships between entities.

Entity-Relationship Signup and view all the answers

Match the SQL commands with their descriptions:

CREATE TABLE = Create a table DROP DATABASE = Delete a database INSERT INTO = Insert rows in a table SELECT = Filter/Search data Signup and view all the answers

What relationship exists between a customer and an order in a relational database?

A customer can make multiple orders, while a single order belongs to one customer. Signup and view all the answers

What is a primary key?

A column that uniquely identifies each row in a table. Signup and view all the answers

What is a foreign key?

A column that refers to the primary key in another table. Signup and view all the answers

Which of the following is a constraint in MySQL?

All of the above Signup and view all the answers

What does the AUTO_INCREMENT feature do?

It allows a unique number to be generated automatically when a new record is inserted. Signup and view all the answers

The default starting value for AUTO_INCREMENT is _____ .

1 Signup and view all the answers

What is the purpose of the WHERE clause in SQL?

To filter records based on specific criteria. Signup and view all the answers

Which of the following operators is NOT a comparison operator in SQL?

<ul> <li></li> </ul> Signup and view all the answers

The LIKE operator is used to specify a pattern search in SQL.

True Signup and view all the answers

Which SQL function would you use to calculate the average value from a column?

AVG() Signup and view all the answers

Match the following SQL functions with their usage:

SUM() = Sum of all values in a column MAX() = Maximum value of a column MIN() = Minimum value of a column AVG() = Average value of a column Signup and view all the answers

What is a data dictionary?

It describes the structure of the database and provides metadata about the data. Signup and view all the answers

Study Notes

Relational Databases Overview

Relational databases are structured collections of data organized into inter-related tables.
Each table consists of rows (tuples) representing records and columns (attributes) defining data properties.
A Database Management System (DBMS) is essential for creating, managing, and updating databases.

Relational Data Model

Relations correspond to tables, with each row representing a unique record sharing a similar structure.
Example of tables includes 'Items' and 'Suppliers' with attributes like ItemID, Name, Supplier, and Price.

SQL Syntax for Table Creation

Use CREATE DATABASE mystore; to initiate a database.
Tables can be created using SQL commands, defining attributes and their data types:
- CREATE TABLE suppliers (supplier_id VARCHAR(2), name VARCHAR(32), phone VARCHAR(11));
- CREATE TABLE items (item_id VARCHAR(2), name VARCHAR(32), supplier VARCHAR(2), price INT);

Keys and Constraints

Constraints define rules for data integrity and reliability in tables.
Primary Key:
- Uniquely identifies each row in a table.
- Must be unique and not null.
Foreign Key:
- References a primary key in another table, establishing relationships between tables.
- A table can have multiple foreign keys.

Entity Relationship Diagram (ERD)

ERDs graphically represent an information system's structures and relationships among entities, useful for data modeling.
Example relationships include:
- Customers can make multiple orders; each order belongs to one customer.
- Items can appear in multiple orders, while an order can involve one item.

SQL Categories

SQL commands are divided into:
- DDL (Data Definition Language): Modifies database structure (e.g., CREATE, DROP, ALTER).
- DML (Data Manipulation Language): Manipulates data within tables (e.g., SELECT, INSERT, UPDATE, DELETE).
- DCL (Data Control Language): Manages access control (e.g., GRANT, REVOKE).
- TCL (Transaction Control Language): Handles transactions (e.g., COMMIT, ROLLBACK).

Basic SQL Commands

Creating and managing databases and tables:
- CREATE DATABASE [DB NAME];
- SHOW DATABASES;
- USE [DB NAME];
- CREATE TABLE [TABLE NAME] ([COLUMN DETAILS]);
- INSERT INTO [TABLE NAME] VALUES (value1, … , value_n);
Modifying tables:
- ALTER TABLE [TABLE NAME] ADD COLUMN [COLUMN_NAME];
- UPDATE [TABLE NAME] SET column1=value1 WHERE condition;
- DELETE FROM [TABLE NAME] WHERE condition;

Important Considerations

Primary key values must be unique in their respective columns.
Foreign keys can only contain values that correspond to existing primary keys in the parent table, ensuring data consistency.

Conclusion

Understanding the relational database structure and SQL commands is fundamental for database management and data integrity.

Relational Databases and MySQL Overview

Constraints define rules for data entry in tables, enhancing accuracy and reliability.
Primary keys uniquely identify each row in a table, while foreign keys link tables by referencing primary keys.

Important MySQL Constraints

UNIQUE: Ensures all values in a column are distinct.
NOT NULL: Prohibits null values in a column.
DEFAULT: Assigns a default value when no value is provided.

Auto Increment Feature

Auto-increment generates a unique number for new records, starting at 1 and increasing by 1.
This feature is crucial for creating unique primary keys in tables.

Example Database Structure

Creation of database called college with tables groups and students.
groups includes a unique groupID, name, and a default profile.
students contains a studentID, name, DOB, and a groupID referencing the groups table.

Inserting Data into Tables

Data inserted into groups with specified values and default handling where necessary.
Standard practice to format dates as YYYY-MM-DD and use quotation marks.
Using timestamps to capture current date and time.

SQL WHERE Clause and Operators

The WHERE clause extracts records matching specific criteria, filtering data queries.
Operators include:
- Arithmetic: +, -, *, /, %
- Comparison: =, !=, <, >, BETWEEN, IN, LIKE
- Logical: AND, OR, NOT

Using Date and Comparison Operators

Dates can be compared using string or numeric values in queries.
BETWEEN operator selects values within a specified range.

Membership and Pattern Matching Operators

IN operator checks for multiple values in a WHERE clause.
LIKE operator searches for patterns in data.

Aggregate Functions

Functions like SUM, MAX, MIN, and AVG perform calculations on data columns.

Data Dictionary

Provides metadata about the database, structured in a spreadsheet format.
Details include names, descriptions of tables, fields, data types, lengths, primary keys, foreign keys, nullability, and uniqueness.
Serves as a reference for understanding the database's structure and contents.

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Description

Explore the fundamentals of relational databases in this lecture. Topics include the relational data model, entities and attributes, keys and relationships, and the entity-relationship diagram. This quiz will help you assess your understanding of these key concepts in information systems.