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Empezar

Luis Saurina, Adrian Martí, Luis Aragón, Daniel Samblás

Relational databases

Instance: Is a piece of data that comes from an entity in the database, for example, if you have the element library.

Three elements:

  • Entitys: People, objects or concepts
  • Attributes: Describe about entitys
  • Relations: Used to create links between entities.

Entity Relationship Model

What is a Entity Relationship Model ?Tool that allows for the simplified representation of how people, objects, or concepts relate to each other.

Cardinality in the E-R

Ways to represent:

  • Rectangles, to represent the entities.
  • Ovals, for attributes.
  • Diamonds or connecting lines to represent relationships between entities and attributes.

Model E-R

Model E-R

WHAT IS RELATIONAL MODEL??

A collection of data organized in a format of rows and columns. Each table represents an entity or a type of object in the system. We can difference in two types of keys: Primary key: For example, a customer's ID number would be the primary key in a customers table:For example, a customer's ID number would be the primary key in a customers table.Foreign key: An attribute in one table that references the primary key in another table. It is used to establish relationships between tables.

Example Model relational

SQL (Structured Query Language) is a language used to manage and manipulate relational databases, allowing operations such as querying, inserting, updating, and deleting data.In SQL there are 3 sublanguages:-DML (Data Manipulation Language)-DCL (Data Control Language)-DDL (Data Definition Language) 1st

SQL

DDL (Data Definition Language) is used to define and modify the structure of databases and tables. This is the first language used when creating your database.

DdL

To DELETE some values

To SELECT values from a table (QUERY)

To insert VALUES into the table

This one if for giving permissions of INSERT

This one if for giving permissions of SELECT

dcl & dml

DDL (Data Definition Language) comes firstDDL is used to define the structure of the database, including creating, modifying, and deleting database objects such as tables, indexes, views, and relationships. Examples of DDL statements include CREATE TABLE, ALTER TABLE, and DROP TABLE.

DCL

DML (Data Manipulation Language)Data Manipulation Language (DML) is used to manipulate and modify the data stored in a database. DML commands are used to insert, update, and delete data in a database.

dml

SQL (Structured Query Language) queries are commands used to interact with relational databases. Queries allow you to extract, insert, update or delete data from a database. SQL is the language that allows us to communicate with these databases.Types of SQL QueriesSELECT: Used to query (extract) data.INSERT: Used to insert new data into the database.UPDATE: Used to update existing data.DELETE: Delete data from the database.

SQL QUERY

Extract information of a table

SELECT:

SQL QUERY

INSERT: Used to insert new data into the database.

SQL QUERY

SQL QUERY

UPDATE: Used to update existing data.

DELETE: Delete data from the database.

SQL QUERY

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