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https://github.com/alexandrospanag/my_sql_projects

My SQL Projects.
https://github.com/alexandrospanag/my_sql_projects

database databases learn mysql sql

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My SQL Projects.

Host: GitHub
URL: https://github.com/alexandrospanag/my_sql_projects
Owner: AlexandrosPanag
License: other
Created: 2021-09-11T08:13:10.000Z (over 3 years ago)
Default Branch: main
Last Pushed: 2023-10-13T04:42:50.000Z (over 1 year ago)
Last Synced: 2024-11-15T13:12:30.592Z (2 months ago)
Topics: database, databases, learn, mysql, sql
Homepage:
Size: 127 KB
Stars: 0
Watchers: 1
Forks: 0
Open Issues: 0
Metadata Files:
- Readme: README.md
- License: LICENSE.md

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README

# My SQL Projects
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⚠️ THIS REPOSITORY WILL BE UPDATED BY 2025 DUE TO LACK OF TIME!!!

Shield: [![CC BY-NC-SA 4.0][cc-by-nc-sa-shield]][cc-by-nc-sa]

This work is licensed under a
[Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License][cc-by-nc-sa].

[![CC BY-NC-SA 4.0][cc-by-nc-sa-image]][cc-by-nc-sa]

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Credits: [@alexandrospanag](https://github.com/alexandrospanag)

✅ LinkedIn Skill Assessment badge
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What is SQL?
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SQL (pronounced "ess-que-el") stands for Structured Query Language. SQL is used to communicate with a database. According to ANSI (American National Standards Institute), it is the standard language for relational database management systems. SQL statements are used to perform tasks such as update data on a database, or retrieve data from a database. Some common relational database management systems that use SQL are: Oracle, Sybase, Microsoft SQL Server, Access, Ingres, etc. Although most database systems use SQL, most of them also have their own additional proprietary extensions that are usually only used on their system. However, the standard SQL commands such as "Select", "Insert", "Update", "Delete", "Create", and "Drop" can be used to accomplish almost everything that one needs to do with a database. This tutorial will provide you with the instruction on the basics of each of these commands as well as allow you to put them to practice using the SQL Interpreter.

SOURCE : http://www.sqlcourse.com/intro.html

Compiler (IDE) used : https://www.mysql.com/downloads/ , https://www.phpmyadmin.net

Most Meterial was based on but altered : https://www.educative.io/courses/introductory-guide-to-sql/ , https://www.sololearn.com/learning/1060 & https://www.w3schools.com/sql/

Other Meterial was based on the valuable book of "Fundementals of Database Systems" by ELMASRI & NAVATHE

We will assume we are an electronic-equipment sales company and we have clients ( or users ) registered to our server with these data :

| Name | Surname | E-mail | Phone | Birthdate | ID Number | Money Spent |
| --------------- | ---------------- | --------------- | --------------- | --------------- | --------------- | --------------- |
| John | Doe | [email protected] | 611 111 1111 | 20/01/2000 | JO1111111 | 50$ |
| Linus| Sebastian | [email protected] | 611 111 1112 | 15/03/2001 | LO1222222| 100$ |
| Nicole | Maria | [email protected] | 611 111 1113 | 23/07/2002 | NI1233333 | 75$ |
| Andreas | San | [email protected] | 611 111 1114 | 30/10/2000 | SA1233333 | 93$ |
| Kim | Wilde | [email protected] | 611 111 1115 | 08/03/2005 | KW1233335 | 250$ |

This is an easy method of how we can add more columns to our database and if we are not entirely sure we want columns in our database, we can remove them

The basic formats are :

ALTER TABLE ADD ;

ALTER TABLE DROP COLUMN ;

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03_ALTER TABLE MODIFY
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If we want to change a column's data type (i.e from int to double ) we use the ALTER TABLE MODIFY ;

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04_UPDATE TABLE
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With the update command , we can easily modify (update) our table with a new value in case something changed or we wish to change it

UPDATE
SET =
WHERE ;

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05_ Temporary Table Example
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Temporary tables can be used to work with intermediate data or results. Also, complex queries with joins or nested queries can be broken up and worked on step-by-step by storing intermediate results in temporary tables.

SOURCE: https://www.educative.io/courses/introductory-guide-to-sql/qVm252ArXPk

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09_ ORDER BY Close
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The ORDER BY clause is followed by the column name on which we intend to sort. This column is called the sort key. By default, the sorting is case-insensitive and in ascending order. Sorting of string columns depends on the character set being used and the collation order.

SOURCE: https://www.educative.io/courses/introductory-guide-to-sql/xoKDKokX3Bz

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10 _ LIMIT Clause
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Usually tables in a production environment have thousands or millions of rows and a select query may return several hundred matched rows. This is problematic because outputting thousands of rows on the console or on a network connection can overwhelm the end-user in the former and is impractical in the latter scenario. The LIMIT clause allows us to restrict the number of rows returned from the result of a select query.

The SQL LIMIT statement restricts how many rows a query returns. A LIMIT statement appears at the end of a query, after any ORDER BY statements. You can start a LIMIT statement at a particular row using the offset argument.

When you’re working in SQL, you may only want to retrieve a specific number of rows from a query.

For example, you may want to retrieve the top three employees based on the number of “employee of the month” awards they have earned. This is easier to read than a list of all employees and how many “employee of the month” awards they have earned.

There is a built-in SQL function that allows you to perform this action: SQL LIMIT. Limit allows you to limit the number of records a query to a certain amount.

SOURCE : https://careerkarma.com/blog/sql-limit/
SOURCE : https://www.educative.io/courses/introductory-guide-to-sql/qAVpzEKg45k

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11_ Deleting Data
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DELETE can be used to delete specific rows , columns or even data or sometimes even entire tables.

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12_ Truncate
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The TRUNCATE statement drops a table and recreates it for faster processing. MySQL doesn't count the number of rows affected and may show the count to be zero or non-zero, but the number doesn't reflect the actual number of rows affected.

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13_ Updating Data
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The UPDATE data can easily change all the columns/row easily & fast.

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14_ Primary Key & Idexes
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