sql.md

SQL discussions

0. What is the difference between SQL and MySQL?
1. What do you mean by DBMS? What are its different types?
2. What are the types of joins in SQL? Give an example for each one.
3. What is a Primary key?
4. What are the different operators available in SQL?
5. What is the need for group functions in SQL?
6. What is a Relationship and what are they?

Please discuss these questions with your partners and post your answers as a comment on this gist when you are finished.

@Geraldmutsw
@LethuM2197

SQL This is a standardized language used to communicate with relational databases. It allows you to perform tasks like creating and modifying tables, retrieving data, and deleting information. Think of it as a set of instructions for interacting with databases.

MySQL: This is a popular open-source relational database management system (RDBMS) that uses SQL as its primary language. It's the software that stores and manages your data based on the instructions you provide using SQL. So, SQL is the language, and MySQL is a specific tool that uses that language.

1. Database Management System.

A DBMS is a software application that allows you to store, organize, retrieve, and manipulate data in a structured way. It provides a central location for managing data and ensures its integrity and consistency. Here are some different types of DBMS:

Relational DBMS (RDBMS): This is the most common type, which stores data in tables with rows and columns and uses SQL for communication.

NoSQL DBMS: This type offers more flexibility for storing unstructured or semi-structured data.

Hierarchical DBMS: Data is organized in a tree-like structure with parent-child relationships.

Network DBMS: Data is organized with records linked to multiple other records, forming a network.

Inner join returns rows with at least one match in both tables.

Left (outer) join returns rows from left table and the matched rows from right table.

Right (outer) join returns rows from right table and the matched rows from left table.

Full (outer) join returns rows with a match in either of the two tables.

A primary key in a table that uniquely identifies each row and column or set of columns in the table. The primary key is an attribute or a set of attributes that help to uniquely identify the tuples(records) in the relational table.

Arithmetic Operators (+, -, , /) for calculations

Comparison Operators (=, <>, <, >, <=, >=) for comparisons

Logical Operators (AND, OR, NOT) for combining conditions

5. The group function in SQL Server provides a powerful tool for performing calculations on groups of rows, allowing you to group data based on specific criteria. This function is important when you want to analyze and summarize information from multiple records in a data structure. The basic group functions are COUNT, SUM, AVG, MAX, and MIN.

6. Relationships define how data tables are linked. They help you organize your data efficiently and retrieve information across different tables.

One-to-One: A single record in one table is associated with exactly one record in another table.

One-to-Many: A single record in one table is associated with multiple records in another table.

Many-to-Many: Multiple records in one table can be associated with multiple records in another table.

Team (Phamela, Ntokozo, Nhlanhla)
Answers.

0. SQL (Structured Query Language) is a standardized language used for managing and manipulating relational databases. MySQL, on the other hand, is a specific relational database management system (RDBMS) that uses SQL to perform database operations. In short, SQL is the language, while MySQL is a database software that uses SQL.

1. A DBMS (Database Management System) is software that interacts with end users, applications,
   and the database itself to capture and analyze data.

Different types of DBMS include:
Relational DBMS (RDBMS): Organizes data into tables with rows and columns (e.g., MySQL, PostgreSQL).

NoSQL DBMS: Handles unstructured data and supports a variety of data models (e.g., MongoDB, Cassandra).

In-Memory DBMS: Stores data primarily in memory for faster access (e.g., Redis, SAP HANA).

Hierarchical DBMS: Organizes data in a tree-like structure (e.g., IBM's IMS).

Network DBMS: Uses a graph structure to represent relationships (e.g., CODASYL DBMS).

2. Types of joins in SQL:

INNER JOIN: Returns records with matching values in both tables.

Example:
SELECT * FROM Orders
INNER JOIN Customers ON Orders.CustomerID = Customers.CustomerID;

LEFT JOIN (or LEFT OUTER JOIN): Returns all records from the left table and matched records from the right table. Unmatched records from the right table will be null.

Example:
SELECT * FROM Orders
LEFT JOIN Customers ON Orders.CustomerID = Customers.CustomerID;

RIGHT JOIN (or RIGHT OUTER JOIN): Returns all records from the right table and matched records from the left table. Unmatched records from the left table will be null.

Example:
SELECT * FROM Orders
RIGHT JOIN Customers ON Orders.CustomerID = Customers.CustomerID;
FULL JOIN (or FULL OUTER JOIN): Returns all records when there is a match in either left or right table. Unmatched records from both tables will be null.

Example:
SELECT * FROM Orders
FULL OUTER JOIN Customers ON Orders.CustomerID = Customers.CustomerID;

CROSS JOIN: Returns the Cartesian product of both tables.

Example:
SELECT * FROM Orders
CROSS JOIN Customers;
SELF JOIN: Joins a table with itself.

Example:
SELECT A., B.
FROM Employees A, Employees B
WHERE A.ManagerID = B.EmployeeID;

3. A primary key is a column or a set of columns in a relational database table that uniquely identifies each row in that table. Here are the key characteristics and purposes of a primary key

4. Arithmetic Operators:
   These are used to perform mathematical operations.

• : Addition

• : Subtraction

• : Multiplication
  / : Division
  % : Modulus (remainder)

2. Comparison Operators:
   These are used to compare two values.
   = : Equal to
   <> or != : Not equal to

: Greater than
< : Less than
= : Greater than or equal to
<= : Less than or equal to

5. Summarizing Data: They allow you to summarize large volumes of data, making it easier to understand and analyze. For example, calculating the total sales, average salary, or maximum marks in a class.
   Performing Calculations on Groups: They enable calculations on subsets or groups of data, which is particularly useful in reporting and data analysis. For instance, calculating the average sales per department or total sales per month.
   Efficiency: Group functions can process and summarize data efficiently, reducing the amount of data that needs to be processed and returned.
   Data Analysis and Reporting: They are critical for data analysis and generating meaningful reports. Aggregating data helps in deriving insights and making informed business decisions.

6.a relationship refers to the connection or association between two or more tables. Relationships are essential for organizing data in a relational database, allowing the database to efficiently store, retrieve, and manage data.

@hunny-bee
@mpilomthiyane97
@kokigod

0. SQL is the Structured Query Language used to create, modify and update databases, whilst MySQL is a database management system that uses SQL

1. DBMS - Database Management System is a software that interacts with end users, applications, and the database to capture and analyze data. It allows users to create, read, update, and delete data in a database. There are hierarchical, relational, network, object-oriented, document-oriented, graph, etc DBMSs

2. Inner join - collects rows from both tables that have at least one match.
   Left join - returns the matching rows from the right table and the rows from the left table.
   Right join - returns rows from the left table that match the rows from the right table.
   Full join - returns rows from either of the two tables that match.

3. A primary key is used to uniquely identify a row in a table

4. IN: Figures out if a value falls inside a range of values.
   BETWEEN: Figures out whether a value falls inside a range of values.
   LIKE: looks for a given pattern within a column.
   EXISTS: Checks if any rows are returned by another query, preventing duplicates

5. Group functions help in SQL for summarizing, analyzing, and reporting data efficiently and effectively. They help transform large datasets into meaningful insights and summaries, facilitating better data-driven decision-making.

6. Relationship is a connection between two or more tables based on one or more columns

Vuyo Ngwane
Thitevhelwi Samuel Masuvhe
Lindokuhle Skosana

0.) Difference between SQL and MySQL:
SQL (Structured Query Language): SQL is a standard language used for managing and manipulating relational databases. It is used to perform tasks such as querying data, updating data, inserting/deleting data, and creating/modifying database structures.
MySQL: MySQL is a specific implementation of a relational database management system (RDBMS) that uses SQL as its query language. MySQL is popular for its ease of use, performance, and wide adoption in web applications.

1.) DBMS and its types:
DBMS (Database Management System): A DBMS is software designed to manage databases. It provides an interface for users and applications to interact with the database by storing, retrieving, and manipulating data.
Types of DBMS:
Relational DBMS (RDBMS): Stores data in a structured format using tables with rows and columns. Examples include MySQL, PostgreSQL, Oracle Database.
NoSQL DBMS: Stores and retrieves data using methods other than the traditional table structures. Examples include MongoDB (document-based), Cassandra (wide-column store), Redis (key-value store).

2.) 3. Types of joins in SQL:
SQL supports different types of joins to combine rows from multiple tables based on a related column between them. The main types are:
INNER JOIN: Returns rows when there is a match in both tables.

SELECT orders.order_id, customers.customer_name
FROM orders
INNER JOIN customers ON orders.customer_id = customers.customer_id;

SELECT customers.customer_name, orders.order_id
FROM customers
LEFT JOIN orders ON customers.customer_id = orders.customer_id;

FULL JOIN (or FULL OUTER JOIN): Returns all rows when there is a match in either left or right table. Returns NULLs where there is no match.

3.) A Primary key is a unique identifier for a record in a database table. It uniquely identifies each record in the table and ensures no duplicate values are entered into the primary key column. It also establishes a relationship between tables (if used as a foreign key in another table).

4.) SQL does provide a number of operators for various data processing and querying activities. -Arithmetic Operators, which are employed in computations with numbers. + - * / %. Operators for comparison: these are used to compare values and provide Boolean results. != or = > \ >= = >. Logical operators are employed to evaluate and combine several circumstances. AND, OR, NOT.

5.) 5. Data Summarization: Group functions let you distill big datasets into insightful synopses. You can get aggregated numbers, such as the total, average, minimum, maximum, or count of particular columns, rather than examining individual rows.
Grouping by Categories: To organize your data into groups according to specific standards, you can utilize group functions in conjunction with the GROUP BY clause. This lets you figure out total values for every group, giving you an idea of how various categories stack up against one another.
Data analysis and reporting: The creation of dashboards and reports depends heavily on group functions. They aid in addressing inquiries such as:
Which customer segment's average order value is that?
Which product category brings in the most money?
What is the size of each department's workforce?
Making decisions: High-level overviews of your data are provided by aggregate results from group functions, which aid in well-informed decision-making. For instance, understanding the typical customer satisfaction score might help direct customer service enhancements.

6.) 6. Within the framework of databases, a relationship establishes the connections between several tables. By creating a connection between data in two or more tables, it makes it possible to compile and obtain relevant data. In SQL, there are three primary kinds of relationships:

One-on-One Connection:

A maximum of one record in each table corresponds to a record in the other table, and vice versa.
Example: A passport is only valid for a single person and can only be held by one individual.
One-to-Many Connection:

A record in one table can have many associations with records in another, but only one association can exist between a record in the second table and a record in the first table.
Example: Although a customer may place several orders, each order is unique to that customer.

Many-to-Many Connection:

Multiple records in the other table may be related with entries in both tables.
For instance, a student may sign up for more than one course, and a course may have more than one student. To manage the associations, this calls for the creation of a junction table, an additional table.

Kgomotso, Selepe, Mpho

0. MySQL is a relational database management system that uses SQL, and SQL is a query programming language that manages RDBMS(Relational Database Management System Software).
1. Database Management System. relational, distributed, hierarchical, object-oriented, and network.
2. INNER JOIN: Returns only the rows that have matching values in both tables.
   SELECT employees.name, departments.department_name
FROM employees
INNER JOIN departments ON employees.department_id = departments.id;

LEFT JOIN (or LEFT OUTER JOIN): Returns all rows from the left table, and the matched rows from the right table. If no match is found, NULL values are returned for columns from the right table.
SELECT employees.name, departments.department_name FROM employees LEFT JOIN departments ON employees.department_id = departments.id;`

RIGHT JOIN (or RIGHT OUTER JOIN): Returns all rows from the right table, and the matched rows from the left table. If no match is found, NULL values are returned for columns from the left table.

SELECT employees.name, departments.department_name FROM employees RIGHT JOIN departments ON employees.department_id = departments.id;`

3.Unique identifier for a record in a relational database table

4. Arithmetic, Bitwise, Comparison, Compound, Logical and String.

5. SQL group functions are crucial for data analysis and summarization. With their help, you may process groups of rows based on shared attributes and display the results in a clearer, more understandable manner.

6. a relationship refers to the connection between two or more tables based on their data. One-to-many, one-to-one, many-to-many

Nokulunga
Sharon

0. MySQL is the underlying technology(software) that stores the data while SQL(database language) is the language you use to read, modify and delete data.

1. DBMS-A Database Management System (DBMS) is software that provides an interface for users and applications to interact with databases, facilitating the processes of data storage, retrieval, management, and manipulation.
   Types - Relational Database Management System(RDBMS)
   Hierarchical Database Management System (HDBMS)
   Network Database Management System (NDBMS)
   Object-Oriented Database Management System (OODBMS)
   Document-Oriented Database Management System (Document Store)
   Columnar Database Management System (Column Store)

2. (INNER) JOIN : Returns records that have matching values in both tables.
   EXAMPLE: An INNER JOIN will return records where there is a match in both tables. In this case, it will match the CustomerID from the Customers table with the CustomerID from the Orders table.

LEFT (OUTER) JOIN : Returns all records from the left table, and the matched records from the right table.
EXAMPLE: A LEFT JOIN will return all records from the Customers table, and the matched records from the Orders table. If there is no match, the result is NULL on the side of the Orders table.

RIGHT (OUTER) JOIN : Returns all records from the right table, and the matched records from the left table.
EXAMPLE: A RIGHT JOIN will return all records from the Orders table, and the matched records from the Customers table. If there is no match, the result is NULL on the side of the Customers table.

Full (outer) join returns rows with a match in either of the two tables
EXAMPLE : A FULL JOIN will return all records when there is a match in either the Customers or Orders table. Records from both tables that do not have matching entries in the other table will still be included, with NULLs in place where data is missing from one of the tables.

3. A primary key, also called a primary keyword, is a column in a relational database table that's distinctive for each record.
   EXAMPLE: StudentId

4. Arithmetic Operators
   addition, subtraction, multiplication, division and modulus

Comparison Operators
equal to( =), not equal to (!=), less than (<), greater than (>)

Logical Operators
AND, OR and NOT

Bitwise Operators
AND (&), OR (|), XOR (^), NOT (~), Shift Left (<<) and Shift Right (>>).

Set Operators
UNION: Combines the results of two queries and removes duplicates
UNION ALL: Combines the results of two queries and includes duplicates
INTERSECT: Returns the common records between two queries
EXCEPT (or MINUS in some databases): Returns the records from the first query that are not in the second query.)

5. Group functions help to summarize large amounts of data

   They enable data analysis by allowing you to compute statistical measures such as averages, counts, and variances.

   By using group functions, you can identify patterns and trends within your data. For instance, you can find out which products are the most
   popular by counting the number of times each product has been sold.

   Group functions are often used in conjunction with the GROUP BY clause to perform calculations on subsets of data. This is useful when
   you want to calculate summary statistics for different groups within a dataset, such as total sales per region or average salary per
   department.

   Group functions allow you to filter groups of data using the HAVING clause, which is similar to the WHERE clause but is used for groups of
   data rather than individual rows.

   Using group functions can significantly improve the efficiency and performance of your queries by reducing the amount of data you need
   to process and return. Instead of retrieving and handling large volumes of raw data, you can retrieve summarized data directly from the
   database.

COUNT(): Returns the number of rows.
SUM(): Returns the sum of a numeric column.
AVG(): Returns the average value of a numeric column.
MIN(): Returns the minimum value.
MAX(): Returns the maximum value.

6. In the context of relational databases, a relationship is a connection or association between two or more tables. Relationships are established based on common columns (keys) that link the tables together. Understanding and defining relationships are crucial for structuring data efficiently and ensuring data integrity.

One-to-One (1:1) Relationship
One-to-Many (1
) Relationship
Many-to-Many (M
) Relationship

Lentsoana Hophney
Wesly
Nonhlanhla Mazibuku

0. SQL is a standardized programming language used for managing and manipulating relational databases.
   ----MySQL is a relational database management system that uses SQL as its query language
1. (Database Management System) is software that enables the creation, management, and use of databases.
   Types -----
   Hierarchical DBMS :Data is organized in a tree-like structure.
   Network DBMS :Data is organized in a graph, allowing multiple parent-child relationships.
   columns.
   Object-oriented DBMS (OODBMS):Data is represented as objects, similar to object-oriented programming.
2. Types of joins in SQL
   a)Inner join: Returns rows that have matching values in both tables.
   b)full- outer join: returns all rows when there is a match in one of the tables and NULL values for columns of the table that does not have a match.
   c)Left-outer join: Returns all rows from left table and matching rows from the right table.
   d)Right- outer join: Returns rows from right table and matching rows from the left table.
   e)cross join: Returns all possible rows combinations from the two tables
   f)self-join: regular join but the table is joining by itself.
   g)Natural join: joins based on
3. A Primary Key is a unique identifier for a record in a database table.
4. a)Arithmetic Operators
   b)Comparison Operators
   c)Logical Operators
   d)String Operators
5. group functions are essential for performing calculations on multiple rows of data to produce a single result. They allow you to summarize large datasets and aggregate datasets using some criteria to uncover insights.6. a relationship refers to the connection between tables that defines how the data in one table is related to the data in another.
6. a relationship refers to the connection between tables that defines how the data in one table is related to the data in another.
   One-to-One Relationship, One-to-Many Relationship, Many-to-Many relationship.