This documents the process it took to execute this project using PostgreSQL.

In this project two tables were used "Customers" and "Orders" for the retail companies database.

Creating the tables.

CREATE TABLE Customers ( CustomerID INT PRIMARY KEY, CustomerName VARCHAR(255), ContactName VARCHAR(255), Country VARCHAR(255) );

CREATE TABLE Orders ( OrderID INT PRIMARY KEY, CustomerID INT, OrderDate DATE, FOREIGN KEY (CustomerID) REFERENCES Customers(CustomerID) );

importing the values into the tables.

(this command was used to import a data set from a csv this applies to both tables)

1. \COPY Orders (OrderID, CustomerID, OrderDate) FROM 'C:/Users/edwin/orders.csv' WITH (FORMAT CSV, HEADER true, DELIMITER ',');
2. \COPY Customers (CustomerID, CustomerName, ContactName,Country) FROM 'C:/Users/edwin/customers.csv' WITH (FORMAT CSV, HEADER true, DELIMITER ',');

Queries used to perform the join the functions.

1. INNER JOIN: Returns records that have matching values in both tables. SELECT Orders.OrderID, Customers.CustomerName, Customers.ContactName, Customers.Country, Orders.OrderDate FROM Orders INNER JOIN Customers ON Orders.CustomerID = Customers.CustomerID;

2. LEFT JOIN: Returns all records from the left table, and the matched records from the right table. SELECT Orders.OrderID, Customers.CustomerName, Customers.ContactName, Customers.Country, Orders.OrderDate FROM Orders LEFT JOIN Customers ON Orders.CustomerID = Customers.CustomerID;

3. RIGHT JOIN: Returns all records from the right table, and the matched records from the left table. SELECT Orders.OrderID, Customers.CustomerName, Customers.ContactName, Customers.Country, Orders.OrderDate FROM Orders RIGHT JOIN Customers ON Orders.CustomerID = Customers.CustomerID;

4. CROSS JOIN: Returns all records from both tables. SELECT Orders.OrderID, Customers.CustomerName, Customers.ContactName, Customers.Country, Orders.OrderDate FROM Orders CROSS JOIN Customers;