There are several methods available when using SQL to mix data from several tables. The JOIN keyword as well as the EXCEPT and INTERSECT keywords are two popular approaches. Together, we will examine each of these techniques and determine their appropriate applications.
SQL JOIN
Combining rows from two or more tables based on a shared column between them is done with the JOIN keyword. By indicating the relationship between the tables, it enables us to access data from several tables. There are various JOIN kinds, each with a distinct function, including FULL JOIN, LEFT JOIN, RIGHT JOIN, and INNER JOIN.
Take into consideration, for illustration, the "Customers" and "Orders." We can utilize the following to obtain the client data and the orders that relate to them.
SELECT Customers.CustomerName, Orders.OrderID
FROM Customers
JOIN Orders ON Customers.CustomerID = Orders.CustomerID;
This query combines the "Customers" and "Orders" tables based on the common "CustomerID" column, returning the customer name and their order ID.
On the other hand, the EXCEPT and INTERSECT keywords are used to compare and combine the result sets of two SELECT statements. The EXCEPT keyword returns the distinct rows from the first SELECT statement that are not present in the second SELECT statement. It is useful for finding the differences between two sets of data.
For example, let's say we have two tables: "Employees" and "Managers." To find the employees who are not managers, we can use the following SQL query.
SELECT EmployeeID
FROM Employees
EXCEPT
SELECT EmployeeID
FROM Managers;This query returns the employee IDs that are in the "Employees" table but not in the "Managers" table.
On the other hand, the INTERSECT keyword returns the distinct rows that are common to both SELECT statements. It is useful for finding the common elements between two sets of data.
For example, consider two tables: "Students" and "ScholarshipRecipients." To find the students who are also scholarship recipients, we can use the following SQL query.
This query returns the student IDs that are present in both the "Students" and "ScholarshipRecipients" tables.
JOIN keyword is used to combine rows from multiple tables based on a
related column, while the EXCEPT and INTERSECT keywords are used to
compare and combine the result sets of two SELECT statements.
Understanding the differences between these keywords and when to use
them is essential for effective data retrieval and analysis in SQL.
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