MySQL is a popular open-source relational database management system (RDBMS) used by developers worldwide. Its syntax is easy to understand and very effective in deleting data from tables. This article will teach the basics and some advanced concepts of using the MySQL Delete Query in SQL.
What is a MySQL Delete Query?
Before we dive into how to use Delete Query, let’s first understand what it is. A Delete Query in MySQL is used to delete one or multiple rows from a table or by using conditions.
The syntax for the Delete Query is as follows:
DELETE FROM <table_name>
WHERE <condition>;
The “DELETE FROM” statement specifies which table you want to delete the data from, and the “WHERE” condition specifies the criteria used to determine which rows to delete.
The Basic Use of MySQL DELETE Query
Now that we’ve seen the syntax of the basic DELETE query, let’s look at an example. Let’s say we have a table named customer
, and we want to delete a record from this table where the CustomerID
is equal to 1.
DELETE FROM customer
WHERE CustomerID=1;
In the above query, we are specifying that we want to delete the row from the customer
table where the CustomerID
is equal to 1.
The MySQL DELETE Query with JOIN
The MySQL Delete Query with JOIN is used to delete data from multiple tables at the same time with a JOIN. Let’s look at an example of how we can do that.
Let’s say we have two tables named customer and orders and we want to delete a record from both tables where customer.CustomerID is equal to the orders.CustomerID and the orders.OrderDate is before a certain date.
DELETE customer, orders
FROM customer
INNER JOIN orders ON customer.CustomerID = orders.CustomerID
WHERE orders.OrderDate < '2021-01-01';
In the above query, we are specifying that we want to delete records from customer and orders tables at the same time with a JOIN. We are using an INNER JOIN to join the two tables and deleting the records where the orders.OrderDate is less than ‘2021-01-01’.
The MySQL DELETE Query with LIMIT
The MySQL Delete Query with LIMIT is used to delete a limited number of records from a table. Let’s take a look at an example.
Let’s say we have a table named student
and we want to delete only two records from this table.
DELETE
FROM student
LIMIT 2;
In the above query, we specify that we want to delete two records from the student
table.
The MySQL DELETE Query with Subquery
The MySQL Delete Query with Subquery allows you to delete records from a table based on the data returned from a subquery. Let’s see how that works.
DELETE
FROM customer
WHERE CustomerID IN (
SELECT CustomerID FROM orders
WHERE OrderDate < '2021-01-01'
);
In the above query, we are specifying that we want to delete records from the customer table where the CustomerID is present in the subquery.
FAQs
Can I recover data from a table after running Delete Query?
No, once a Delete Query is executed, the data is permanently removed from the table and cannot be recovered
Can I use Delete Query with Triggers?
Delete Query can be used with Triggers to delete records from other tables.
Can I delete multiple rows using the MySQL Delete Query?
Yes, you can delete multiple rows by specifying multiple conditions in the WHERE clause.
Can I use Delete Query with Foreign Key Constraints?
Yes, you can use Delete Query with Foreign Key Constraints to delete records from both tables.
How can I prevent accidental deletion of data using Delete Query?
You can prevent accidental deletion of data by adding WHERE clause with a condition explicitly to identify the data you want to delete.
Conclusion
In this article, we learned how to use the basic and advanced concepts of MySQL Delete Query in SQL. We learned how to delete data from single and multiple tables, delete limited records, and how to use a subquery with the Delete Query.
It’s essential to take plenty of care and attention when executing a Delete Query. Accidentally deleting records could lead to data loss, so make sure you back up your data before running the queries.
If you want to learn more about MySQL and deletes queries, here are some trusted sources to help you get started:
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