Lesson 16 - Databases and Simple SQL Queries

What is a database?

is an organized collection of dat that is kept in a computer system

SQL

a relational database system that uses tables to store structured data. Designed for managing and manipulating data with relational database management systems.

NoSQL

a non-relational database system that stores data using different models instead of tables. Ideal for applications that need to handle lots of data, like social media, or big data.

SQL database examples

MYSQL, Oracle Database, Microsoft SQL server

NoSQL database examples

Mongo DB, Casandra, Amazon DynamoDB

SQL Schema

reflects what tables are in database, what columns they have and how they are related.

Primary key

is a field in a table which uniquely identifies each row in a table. Must contain unique values. Cannot have NULL values.

Foreign key

is used to link two tables together.

Row

collection of fields that make up a record

DBMS

Database Management System

DBMS

designed to create, manage, and manipulate databases. It serves as an interface between the database and its users or application programs, enabling users to efffciently store, access, and modify data.

Column

set of data values of a particular simple type

Table

collection oof data elements

SQL Keywords - SELECT

Retrieves data from database

SQL Keywords - FROM

Specifies the able from which to retrieve data

SQL Keywords - WHERE

Filters records to select only those that meet a specific condition.

SQL Keywords - ORDER BY

sorts the result set in ascending or descending order

SQL Keywords - GROUP BY

groups rows based on specified columns for aggregate function calculations

SQL keyword =

compares two values for equality

SQL keyword <

checks if the value on the left is less than the value on the right

SQL keyword >

checks of the value on the left is greater than the value on the right

SQL keyword - AND

Combines two conditions and returns true if both conditions are true

SQL keyword - OR

Combines two conditions and returns truw if at lease one of the conditions is true

SQL keyword - IN

Checks if a value is within a list of specified values