MySQL Union vs Join

MySQL UNION and JOIN are both database operations used to work with data from multiple tables, but they serve different purposes.

MySQL UNION:

• UNION is used to combine the result sets of two or more SELECT queries into a single result set.
• It is typically used when you want to retrieve rows from multiple tables with similar structures and combine them into a single result set.
• The UNION operation removes duplicates by default, but you can use UNION ALL to include duplicates.
• UNION does not require a common column or relationship between the tables; it simply stacks the result sets on top of each other.

Example of UNION:

SELECT column1 FROM table1
UNION
SELECT column1 FROM table2;

MySQL JOIN:

• JOIN is used to retrieve data from multiple tables based on a related column between them.
• It allows you to combine rows from two or more tables using a common column (usually a primary key or foreign key) as the joining condition.
• There are different types of joins in MySQL, such as INNER JOIN, LEFT JOIN, RIGHT JOIN, and FULL JOIN, each with its own characteristics in terms of the inclusion of matching and non-matching rows.
• JOIN is used to create more complex result sets by combining data from different tables.

Example of JOIN (INNER JOIN):

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

In summary:

• Use UNION to combine rows from multiple tables with similar structures into a single result set.
• Use JOIN to retrieve data from multiple tables based on a related column, allowing you to work with related data and create complex result sets.
• The choice between UNION and JOIN depends on the specific requirements of your query. If you need to combine data from unrelated tables, use UNION. If you need to retrieve data based on relationships between tables, use JOIN.