Why does MySQL not recommend using join?

MySQL is a popular open source relational database management system that supports a variety of operations, including data storage, query, update, and deletion. In MySQL, it is a very common method to use the JOIN statement for relational query. However, some MySQL developers do not recommend using the JOIN statement because it can cause query performance degradation, especially on large databases. So, why does MySQL not recommend using the JOIN statement? This article will explore this question.

What is the JOIN statement?

In MySQL, the JOIN statement is used to join the data in two or more tables to implement associated queries. JOIN statements are often used to query tables that contain related data, for example, to query all orders for a person or to query all products in an order.

MySQL supports several JOIN types, including INNER JOIN, LEFT JOIN, RIGHT JOIN, and FULL OUTER JOIN. Among these JOIN types, INNER JOIN is the most commonly used type. It returns matching rows from both tables, whereas LEFT JOIN, RIGHT JOIN, and FULL OUTER JOIN return rows of different types. While the JOIN statement can be very efficient for querying related data, it can also lead to poor query performance, especially on large databases.

Performance issues with JOIN statements

The performance problems of the JOIN statement mainly focus on the following two aspects:

1. In the case of a large amount of data, the JOIN statement may cause the query speed to slow down

When the amount of data in a table increases, the query speed of the JOIN statement may decrease. This is because the JOIN statement needs to perform a lot of data matching operations to find the relevant rows. When the amount of data in the table is very large, these matching operations can be very time-consuming, causing the query speed to slow down.

1. JOIN statements may cause an increased load on the MySQL server

When querying large amounts of data using JOIN statements, the load on the MySQL server may increase. This is because the JOIN statement needs to perform a large number of data matching operations, thus consuming the computing resources and memory resources of the server. If the MySQL server does not have enough resources to handle these operations, it may become very slow or crash.

Optimization of the JOIN statement

Although the JOIN statement may cause query performance to degrade, there are some optimizations that can be made to improve its performance. Here are some optimization methods:

1. Create an index on the table

Creating indexes on tables can greatly improve the performance of JOIN statements. An index is a special data structure that helps MySQL quickly locate data in a table. When using the JOIN statement, if the data in the table has been indexed, then MySQL can match the relevant rows more quickly, thereby improving the query speed.

1. Limit the number of rows returned by a query

When using the JOIN statement to query data, you can limit the number of rows returned to improve query performance. You can use the LIMIT clause to limit the number of rows returned by a query. This reduces the amount of data processed by the MySQL server, thereby increasing query speed.

1. Use subqueries instead of JOIN statements

Sometimes subqueries can be used instead of JOIN statements to query related data. A subquery is a query statement that can be nested within other query statements. When subqueries are used, MySQL only needs to execute a single query, which reduces data matching operations and improves query speed.

1. Use caching technology

MySQL supports caching technology, which can cache frequently used query results to avoid repeated execution of the same query. This can greatly improve query speed, especially for frequently used queries. Using caching technology can reduce server load and improve query performance.

in conclusion

In MySQL, the JOIN statement is a very useful query method, which can connect the data in two or more tables to realize association query. Although the JOIN statement may cause query performance to degrade, some optimization methods can be taken to improve its performance, such as creating indexes in the table, limiting the number of rows returned, using subqueries instead of JOIN statements, and using caching techniques.

Therefore, although MySQL does not recommend using the JOIN statement, it is still a very useful query method. MySQL developers should choose to use the JOIN statement or other query methods according to the actual situation to achieve the best query performance and effect. At the same time, MySQL developers should also understand how to optimize the JOIN statement in order to improve its performance when using the JOIN statement.