SQL Basic 1

Client/Server Architecture

After the era of mainframes, the shift was towards client/server systems where a main computer (server) is accessible from the network and PCs, allowing read access to be performed over the network.

SQL Basics

SQL involves relational databases divided into tables related by common key fields, allowing data to be broken down into manageable units for easier maintenance and optimization. Tables consist of fields (columns) and records (rows) containing specific information.

SQL Commands

SQL commands include Data Definition Language (DDL) for creating and restructuring database objects, Data Manipulation Language (DML) for inserting, updating, and deleting data, Data Query Language (DQL) for focusing on querying data, Data Control Language (DCL) for controlling database access, and Transaction Control Commands for managing transactions.

Entity-Relationship Diagrams

ERD relationships illustrate attributes within entities, which translate to tables and columns in a database. Attributes become columns when building tables using SQL.

Database Life Cycle

The database life cycle involves stages like development, testing, and production. Relationships in databases can be one-to-one, one-to-many, many-to-many, or recursive, each defining different record interactions.

Normalization

Normalization is a technique to eliminate redundant data and optimize relationships between data entities. It involves organizing data into logical entities and tables to reduce data redundancy and improve query speed, typically following the first, second, and third normal forms.

Understanding the SQL

A relational database is a database that is divided into logical unit called tables these tables are related to one and another with in the database a relational database allows the data to be broken down logics smaller manageble units easier maintaine and more option to the data optimiztion

the tables are adequtely related such that it can be retrived in a single query

whic are having a comman key fields

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every table is divided into small entites called fields

a field is a column in a table that is designed to mauntian specific information

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records are also called rows of data in a horizontal entity in table

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Primary key

Foregin key

NULL is the term that is used to represent the missing value and a null value in a table is a value in a field that appers to be blank

there are logical elements which might include the elements like

entities

attribuites

relationships

information

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Database schema

a schema is a group of related object in a database. a schema is owned by a single database user and objects

type of SQL Commands

data definatioan language

data manipulation language

data query language

data control language

data admin commands

transaction control commands

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database structure.

DDL it is a part that a enables a database user to create and restructure database obj like

CREATE

DELETE

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CREATE, ALTER, DROP

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DML COMMAND ARE LIKED TO INSERT UPDATE DELETE A DATA

INSERT, UPDATE, DELETE

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DQL THIS IS TO CONCENTRATE FOCUS OF SQL

SELECT

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DCL are THE CONTROL COMMAND IN SQL WHICH ARE USED TO DATABASE

alter

grant

revoke

create synonym

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transational control commands are

commit

rollback

savepoint

set transaction

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Entity and relationships

ERD relationships illustrate with a database as the attibutes with each entity.

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from a logical stand point s the entity and attributes in a diagrame will evetual;y become the table and columns in a database

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attributes will become columns when you build the tables using the SQL

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Database Life cycle

development

test

production

relationship

there are

one to one relationship

one to many relatiinship

many to many relationship

recursive relationship

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One to one relationship

in a one to one relationship one record in a table is related to the only one record in another table

one to many

in a one to many relationship one record is related to one or many records in the anothe table

Many to many relation

we have two many to many relationship in another table

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referencial integriti is defined as the pertain to parent an child relation in a realational database

it can be taken as primary key and foreign key

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primary key

a primary key is simply a constaint placed on a column in a table that identifies each data value in that column or field as unique

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forgine key = primary key of the secondary table

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hour - 7

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Normalization

it is technique that will eliminate the redundent data and optimuze the relationship between the data entities

the same data that is present in one or more table which can lead to high data space usage reduce speed of the query

there are three most common normal forms in the normalization

the first normal form

the second normal form

the third normal form

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in the fnf

the objective is that divide the data into logical entities and ultimately table such that there is no repeted data groups of the table

inside one of the large table you have three small and more manageble tables