The execution order of data queries and data updates in PHP and MySQL indexes and their impact on performance

The execution order of data query and data update of PHP and MySQL indexes and their impact on performance

Introduction:
In development, PHP and MySQL are Commonly used combinations, MySQL is a relational database management system, and PHP is a scripting language used to develop web applications. When processing large amounts of data, the use of indexes is critical to the performance of query and update operations. This article will discuss the execution order of data queries and data updates in PHP and MySQL indexes and the impact on performance, and provide specific code examples.

1. Execution order of data queries and its impact on performance
When performing data queries, MySQL will prioritize index search operations to improve query efficiency. The execution sequence of data query can be simply divided into three steps: index scanning, data reading and result return. The following is a specific example:

$query = "SELECT * FROM users WHERE age > 18";
$result = mysqli_query($connection, $query);
while ($row = mysqli_fetch_assoc($result)) {
    echo $row['name'] . '<br>';
}

In the above code, the query statement SELECT * FROM users WHERE age > 18 means querying the information of users whose age is greater than 18. When performing a query operation, MySQL will first search the index of the age field, find records that meet the conditions, and read the corresponding data and return it to PHP.

The use of indexes has an important impact on the performance of data queries. If the fields in the table are not indexed, MySQL will scan the entire table and check whether the conditions are met record by record, which will lead to low query efficiency. If a suitable index is established, the number of data scans can be greatly reduced and query efficiency improved.

When designing an index, the frequency of queries and the efficiency of queries need to be considered comprehensively. Too many indexes may result in increased index maintenance overhead and may impact performance when updating data. Therefore, when selecting index fields, you should evaluate based on actual business needs and query conditions, and select appropriate fields for indexing.

2. Execution order of data update and its impact on performance
Data update refers to the modification operation of existing data in the table, including insert, update and delete. The execution sequence of data updates can be simply divided into two steps: index update and data modification. The following is a specific example:

$query = "UPDATE users SET age = 20 WHERE id = 1";
$result = mysqli_query($connection, $query);

In the above code, the update statement UPDATE users SET age = 20 WHERE id = 1 means that the age of the user with id 1 is modified to 20 . When performing an update operation, MySQL will first search the index of the id field, locate the record that needs to be modified, and modify the corresponding data.

The impact of data updates on performance is closely related to the use of indexes. If the fields in the table are not indexed, and the conditions for the update operation do not use indexed fields, MySQL needs to scan the entire table and perform the update operation record by record, which will lead to low update efficiency. If a suitable index is established and the conditions of the update operation use the index field, the number of data scans can be greatly reduced and the update efficiency can be improved.

At the same time, data updates will also affect the maintenance cost of the index. When an index field in the table is modified, MySQL needs to update the index, which will consume a certain amount of time and resources. When updating data, you should try to avoid a large number of update operations on index fields to reduce the cost of index maintenance.

In summary, the use of indexes has an important impact on the performance of data query and data update. When performing data queries, you can improve query efficiency by establishing appropriate indexes; when performing data updates, you need to comprehensively consider the use and maintenance costs of the index to improve update efficiency.

Conclusion:
In the development of PHP and MySQL, the use of indexes is crucial to the performance of data query and data update. By establishing appropriate indexes, query efficiency and update efficiency can be improved. When designing indexes, the frequency and efficiency of queries need to be comprehensively considered to avoid too many indexes; at the same time, when updating data, try to avoid a large number of update operations on index fields to reduce the cost of index maintenance. Only by selecting and using indexes rationally can the performance of the system be maximized.

Reference code:
The following is a sample code to create an index and update data:

Create index:
ALTER TABLE users ADD INDEX idx_age(age);

Update data:
UPDATE users SET age = 20 WHERE id = 1;

The above code is for example only, please modify and use it appropriately according to the actual situation.

References:

1. Practical joint development of PHP and MySQL, written by Huang Dongjun, People's Posts and Telecommunications Publishing House, 2017
2. Practical practice of high-performance tuning of MySQL, Basis Author, Tsinghua University Press, 2018

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