Union Operator in MariaDB
Last Updated :
02 Feb, 2024
MariaDB is an Open-Source Database system and MariaDB offers similar security features to MySQL, including access control, user authentication, and encryption. UNION operator is a fundamental part of MariaDB, a well-known database system. The UNION operator merges results from different SELECT queries. In this article, We will understand the Union Operator in MariaDB along with the syntax, its practical examples, the difference between the join and Union, and so on.
MariaDB UNION Operator
In MariaDB, the UNION operator joins two or more SELECT queries into one set. It's useful when we need to merge data from several tables or conditions. The UNION operator automatically removes any duplicate rows, simplifying the data.
Syntax:
SELECT column FROM table1
UNION
SELECT column FROM table2;
Explanation:
- SELECT: It defines the columnsthat we want to retrieve from the tables.
- table1, table2 : Represents the tables from which you're fetching the data.
- UNION : Indicates the UNION operation to combine the results of the two SELECT statements.
Remember, every SELECT statement in the UNION should have matching column counts and types. They should also follow the same order. The UNION operator helps merge different data sources in MariaDB. This enabling more complex and insightful data analysis and reporting.
Example of Union Operator in MariaDB
To understand the Union Operator in detail we need some tables on which we will perform various operations related to the Union Operator. Here we have created a two tables called orders and returns table.
orders table looks like:
table ordersreturns table looks like:
table returns Example 1: Combining Orders and Returns
Let's Combine the order information (order_id, customer_id, product_id, order_date) from the "orders" table with the return information (return_id, customer_id, product_id, return_date) from the "returns" table, by removing the duplicates.
Query:
SELECT order_id, customer_id, product_id, order_date FROM orders
UNION
SELECT return_id, customer_id, product_id, return_date FROM returns;
Output:
Output1Explanation: In this select query that returns the combined data into a single result set. It gives us info on both successful orders and returns. Each row will show details like the order_id/return_id, customer_id, product_id, and the related dates.
Example 2: Combining Orders and Returns for a Specific Customer
Let's Retrieve all records from the "orders" table and the "returns" table where the customer ID is 1, combining the results while removing duplicates.
Query:
SELECT * FROM orders WHERE customer_id = 1
UNION
SELECT * FROM returns WHERE customer_id = 1;
Output:
search outupt 2Explanation: This query retrieves data for customer_id 1. It fetches data from two tables: orders and returns. It shows all orders and returns associated to that customer.
Example 3: Combining Orders and Returns for a Specific Product
Let's Retrieve all records from the "orders" table and the "returns" table where the product ID is 104, combining the results while removing duplicates.
Query:
SELECT * FROM orders WHERE product_id = 104
UNION
SELECT * FROM returns WHERE product_id = 104;
Output:
output3Explanation: This query fetches data about product_id 101. It gets information from orders and returns tables. It shows all orders and returnes for this specific product.
Example 4: Combining Orders and Returns Sorted by Date
Let's Combine all records from the "orders" table and the "returns" table, removing duplicates, and then order the results based on the "order_date" column.
Query:
(SELECT * FROM orders)
UNION
(SELECT * FROM returns)
ORDER BY order_date;
Output:
output 4Explanation: This query joins data about orders and returns. The results get sorted by the order date so we see the orders and returns in time order.
Difference Between the UNION and JOIN Operator
|
Purpose
| It Combines the results of two or more SELECT queries into a single result set, eliminating duplicates.
| It Retrieves data from multiple tables based on a related column between them.
|
Syntax
| SELECT column1, column2 FROM table1 UNION SELECT column1, column2 FROM table2;
| SELECT column1, column2 FROM table1 INNER JOIN table2 ON table1.column = table2.column;
|
Number of Tables
| It Can combine results from multiple tables.
| It Typically involves joining two tables.
|
Result Set
| It Combines rows from both queries, removing duplicates.
| It Combines columns from matched rows of both tables.
|
Performance
| It may have performance overhead, especially if there are many duplicate rows.
| It generally more efficient for retrieving related data from multiple tables.
|
Duplicate Handling
| It removes duplicate rows from the result set by default.
| It does not handle duplicate rows by default. You may need to use DISTINCT or other methods to remove duplicates.
|
In short UNION and JOIN like tools for data. UNION merges results of two or more SELECT queries, removing duplicate rows automatically. JOIN, however, retrieves data from numerous tables based on a related column. Generally, JOIN is used to get data from two or more tables using a common column. While UNION is good at dealing with many tables and deleting duplicates. To remove duplicates with JOIN, you'll need to use DISTINCT.
Conclusion
This article shows how the MariaDB UNION operator handling data from several tables. We learned it can merge results from different SELECT queries into one result. We also saw how to use UNION operator in MariaDB or can do that too with an example. Understanding the MariaDB UNION operator helps database pros properly manage data.
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