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‎legacy/databases/README.md‎

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# databases
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# Databases
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TODO
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## Relational and Non-Relational Data and Database Systems
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### About
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This three-week program aims to introduce the fundamental concepts of data entities and data storage.
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### Key Objectives
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By the end of this module, students should have a familiarity with and basic understanding of the following:
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- Entities
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- The relational model
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- The Structured Query Language (SQL)
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- The construction of a database system
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- MySQL as an example of a relational database system
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- Non-relational data and NoSQL
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- MongoDB as an example of a NoSQL database
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## Lesson Plan
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### [Lesson 1](lesson1/): Retrieving Data
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In this class, students will be introduced to retrieving data from a MySQL database using SELECT queries.
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Objective: Students should be able to retrieve data from a database table using SELECT statements that include WHERE, GROUP BY, ORDER BY, LIMIT, and JOIN.
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### [Lesson 2](lesson2/): Data Models, Relationships, and Schemas
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In this class, the students will learn how to use more complex SQL queries to retrieve information across tables, and interact with data including write operations.
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Objective: the students should be able to build CRUD functionality using SQL statements, including INSERT INTO, UPDATE and DELETE. The students should also be able to create an entity relationship diagram based on a qualitative description of data requirements, and translate that into a MySQL database schema.
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### [Lesson 3](lesson3/): Security and Non-Relational Databases
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In the final week, the students will be introduced to SQL injection and how to use MySQL permissions to avoid it. MongoDB, as an example of a non-relational database, will also be introduced, as well as the benefits and drawbacks of relational and non-relational models.
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Objective: the students should know how SQL injection happens, and how to define user permissions in MySQL to avoid part of it. The students should also be able to compare and contrast relational (like MySQL) and NoSQL databases (considering their benefits and drawbacks).

‎legacy/databases/lesson1/README.md‎

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# Lesson 1: Retrieving Data
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In this class, students will be introduced to relational data terminology (row, column), the function of a primary key, and retrieving data from a MySQL database using SELECT queries.
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Objective: Students should be able to retrieve data from a database table using SELECT statements that include WHERE, GROUP BY, and ORDER BY.
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## Pre-Class Preparation
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Before the class you should Docker and MySQL VScode plugin on your computer.
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### Installing Docker and the MySQL VScode plugin
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- Install docker by following the instructions here: <https://drive.google.com/file/d/1zVV9SyqxkHPnieQ3f2gned7JAljnvZtt/view?usp=drive_link>
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- Install the MySQL VSCode plugin by following the instructions here: <https://drive.google.com/file/d/1FS50CCVUgRAXe9SfS8IMyCY9tFqCXna8/view?usp=drive_link>
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### To learn what Docker is, you can read these articles
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- <https://medium.com/@SaadAAkash/docker-for-dummies-literally-ab3fc6362d5f>
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- <https://www.freecodecamp.org/news/docker-simplified-96639a35ff36/>
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Docker is widely used by software developers these days, i’d say it’s been a
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game changer, so it’s good for you if you at least know what it is :slightly_smiling_face:
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## Main Topics
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- The relational model of data
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- A 'database' vs. a 'DBMS' (database management system)
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- The concept of a schema
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- The properties of an 'entity' (or 'row')
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- Basic entity relationship diagrams
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- A basic SELECT statement
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- Constructing more complex SELECT statements
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- Pattern matching with LIKE
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- Limiting and ordering results with LIMIT and ORDER BY
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- Grouping results with GROUP BY
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- Aggregate functions like AVG, COUNT, SUM, MIN and MAX
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- JOIN
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- Selecting composite data from multiple tables
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- Compare JOIN WHERE with cartesian product
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- Naming Conventions: UpperCamelCase/PascalCase, lowerCamelCase, snake_case, hnHungarianNotation/HNHungarianNotation
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- Character Sets in Databases (hint: always use UTF-8 encoding, called 'utf8mb4' in MySQL)
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## Reference Material
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- [TutorialsPoint MySQL Introduction](http://www.tutorialspoint.com/mysql/mysql-introduction.htm)
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- [w3schools tutorial (easy to find how specific commands work)](https://www.w3schools.com/sql/default.asp)
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- [Official MySQL Documentation](https://dev.mysql.com/doc/refman/8.0/en/)
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- [Official MySQL Tutorial (pretty dense)](https://dev.mysql.com/doc/refman/8.0/en/tutorial.html)
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- [Joel Spolsky - Character Sets and Unicode](https://www.joelonsoftware.com/2003/10/08/the-absolute-minimum-every-software-developer-absolutely-positively-must-know-about-unicode-and-character-sets-no-excuses/)
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## Homework
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### Start the homework
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Need to brush up on the homework setup process? Check [this](https://github.com/HackYourFuture-CPH/Git/blob/main/homework-submission.md) out before you get into some git confusion!
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### The task
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Design queries that retrieve the following data sets. Compare with classmates to see if your answers are correct.
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1. Find out how many tasks are in the task table
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2. Find out how many tasks in the task table do not have a valid due date
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3. Find all the tasks that are marked as done
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4. Find all the tasks that are not marked as done
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5. Get all the tasks, sorted with the most recently created first
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6. Get the single most recently created task
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7. Get the title and due date of all tasks where the title or description contains **database**
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8. Get the title and status (as text) of all tasks
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9. Get the name of each status, along with a count of how many tasks have that status
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10. Get the names of all statuses, sorted by the status with most tasks first
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Watch the previous session recorded on video here:
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Part 1 : <https://www.youtube.com/watch?v=gAeww1z5774>
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Part 2 : <https://www.youtube.com/watch?v=u77w6Lw2gOY>
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Part 3 : <https://www.youtube.com/watch?v=Mag9n6olmRU>
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### Hand in homework
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Need to brush up on the homework hand-in process?
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Check [this resource](https://github.com/HackYourFuture-CPH/Git/blob/main/homework-submission.md) to remember how to hand in the homework correctly!

‎legacy/databases/lesson1/SQL Joins.pdf‎

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‎legacy/databases/lesson1/SQL-Joins.md‎

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# SQL Joins
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> An SQL JOIN clause is used to combine rows from two or more tables,
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> based on a common field between them.
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There are different types of joins available in SQL:
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**INNER JOIN**: returns rows when there is a match in both tables.
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**LEFT JOIN**: returns all rows from the left table, even if there are no matches in the right table.
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**RIGHT JOIN**: returns all rows from the right table, even if there are no matches in the left table.
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**FULL JOIN**: It combines the results of both left and right outer joins.
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The joined table will contain all records from both the tables and fill in NULLs for missing matches on either side.
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**SELF JOIN**: is used to join a table to itself as if the table were two tables, temporarily renaming at least one table in the SQL statement.
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**CARTESIAN JOIN**: returns the Cartesian product of the sets of records from the two or more joined tables.
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WE can take each first four joins in Details :
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## Our example data
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We have two tables with the following values.
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`TableA`:
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id firstName lastName
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.......................................
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1 arun prasanth
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2 ann antony
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3 sruthy abc
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6 new abc
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`TableB`:
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id2 age Place
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................
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1 24 kerala
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2 24 usa
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3 25 ekm
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5 24 chennai
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## Details
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### INNER JOIN
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**Note** :it gives the intersection of the two tables, i.e. rows they have common in TableA and TableB
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Syntax
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SELECT table1.column1, table2.column2...
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FROM table1
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INNER JOIN table2
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ON table1.common_field = table2.common_field;
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Apply it in our sample table :
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SELECT TableA.firstName,TableA.lastName,TableB.age,TableB.Place
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FROM TableA
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INNER JOIN TableB
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ON TableA.id = TableB.id2;
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Result Will Be
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firstName lastName age Place
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..............................................
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arun prasanth 24 kerala
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ann antony 24 usa
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sruthy abc 25 ekm
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### LEFT JOIN
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**Note** : will give all selected rows in TableA, plus any common selected rows in TableB.
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Syntax
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SELECT table1.column1, table2.column2...
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FROM table1
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LEFT JOIN table2
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ON table1.common_field = table2.common_field;
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Apply it in our sample table :
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SELECT TableA.firstName,TableA.lastName,TableB.age,TableB.Place
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FROM TableA
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LEFT JOIN TableB
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ON TableA.id = TableB.id2;
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Result
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firstName lastName age Place
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...............................................................................
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arun prasanth 24 kerala
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ann antony 24 usa
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sruthy abc 25 ekm
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new abc NULL NULL
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### RIGHT JOIN
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**Note** : will give all selected rows in TableB, plus any common selected rows in TableA.
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Syntax
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SELECT table1.column1, table2.column2...
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FROM table1
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RIGHT JOIN table2
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ON table1.common_field = table2.common_field;
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Apply it in our sample table :
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SELECT TableA.firstName,TableA.lastName,TableB.age,TableB.Place
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FROM TableA
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RIGHT JOIN TableB
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ON TableA.id = TableB.id2;
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Result
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firstName lastName age Place
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...............................................................................
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arun prasanth 24 kerala
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ann antony 24 usa
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sruthy abc 25 ekm
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NULL NULL 24 chennai
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### FULL JOIN
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**Note** :It will return all selected values from both tables.
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Syntax
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SELECT table1.column1, table2.column2...
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FROM table1
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FULL JOIN table2
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ON table1.common_field = table2.common_field;
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Apply it in our sample table :
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SELECT TableA.firstName,TableA.lastName,TableB.age,TableB.Place
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FROM TableA
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FULL JOIN TableB
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ON TableA.id = TableB.id2;
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Result
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firstName lastName age Place
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...............................................................................
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arun prasanth 24 kerala
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ann antony 24 usa
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sruthy abc 25 ekm
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new abc NULL NULL
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NULL NULL 24 chennai
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## Interesting Fact
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For INNER joins the order doesn't matter
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For (LEFT, RIGHT or FULL) OUTER joins,the order matter
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Better to go check this **[Link][1]** it will give you interesting details about join order
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[1]: https://stackoverflow.com/questions/9614922/does-the-join-order-matter-in-sql

‎legacy/databases/lesson1/class_exercises.md‎

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# Class exercises
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Implement the following queries:
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1. Select the names and phones of all users;
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2. Select the name of the user with `id=10`;
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3. Find how many users exist in the database;
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4. Select the names of the first 5 users in the database;
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5. Select the names of the last 3 users in the database;
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6. Sum all the ids in the `user` table;
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7. Select all users and order them alphabetically by name;
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8. Find all tasks that include `SQL` either on the title or on the description;
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9. Find the title of all tasks that the user `Maryrose` is responsible for;
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10. Find how many tasks each user is responsible for;
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11. Find how many tasks with a `status=Done` each user is responsible for;

‎legacy/databases/lesson1/hyf_db_eer_diagram.png‎

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