mysql optimization query node

With the continuous development of the Internet and big data technology, MySQL database has become the first choice of many developers and data analysts. MySQL provides powerful functions, but it is still difficult for novices to learn and use MySQL. Among them, MySQL query node is an easily overlooked but very important concept. This article will introduce you to the concept and function of MySQL query nodes and how to optimize query nodes to improve MySQL query speed.

1. The concept of MySQL query node

MySQL query node actually refers to when executing a SQL statement. MySQL will establish a query syntax tree during the execution of the statement. The query syntax Each node in the tree is a subquery node. These subquery nodes are called MySQL query nodes in the order in which they are executed.

MySQL query node is a tree structure, each node in which can be regarded as a SELECT statement. Because during the execution of a SQL statement, MySQL may contain multiple subqueries, and these subqueries will form a query node. For example, the following SQL statement:

SELECT * FROM (
    SELECT * FROM `users` WHERE `age` > 20
) as `a`
WHERE `a`.`name` LIKE '%Tom%'

Among them, the entire SQL statement contains two subqueries, and its query node is a binary tree:

                    第1层
                 Query#1
                   /    \
                  /      \
                 /       \
              第2层      第2层
           SELECT#1  SELECT#2
             /   \        |
            /     \       |
           /       \      |
       第3层      第3层   |
      SELECT#3   WHERE#1  |
         /           |    |
        /            |    |
       /            AND#1 |
   第4层        /           \
  FROM#1     /             \
          users#1         a#1
        WHERE#2
        /     \
     age>20   #TRUE

2. The role of MySQL query node

The MySQL query node is an optimization tool within MySQL, which can help MySQL optimize the execution process of query statements. When executing a MySQL query statement, MySQL will convert the query statement into query nodes, and then execute the query statement according to the execution order of the query nodes. The functions of query nodes are as follows:

1. Improve query efficiency

MySQL query is a relatively complex operation, so a good query optimization strategy is required. Query nodes can help MySQL optimize the execution process of query statements and improve query efficiency.

2. Reduce MySQL’s disk access

When querying large data sets, MySQL queries often require frequent disk access, and this disk access will seriously affect Query efficiency. Query nodes can help MySQL improve cache utilization, thereby reducing MySQL's access to disk.

3. Analyze query performance

The query node can help MySQL accurately analyze the execution performance of query statements, thereby helping developers better optimize performance.

3. Optimization of MySQL query nodes

The optimization of MySQL query nodes can start from strictly limiting query nesting, optimizing subqueries, and using JOIN as much as possible. The following are specific suggestions:

1. Limit the number of query nesting levels

The deeper the nesting level of the query statement, the greater the number of query nodes and the query efficiency. will be lower. Therefore, it is recommended not to nest more than 3 levels of subqueries in the query statement to avoid adverse effects on performance.

2. Optimizing subqueries

When performing subqueries, you should try to use JOIN instead of IN or EXISTS keywords. Because IN and EXISTS queries will cause MySQL to execute two queries, JOIN queries only need to execute one query. At the same time, JOIN query can improve query efficiency by optimizing query nodes.

3. Try to use JOIN

When performing multi-table queries, you should try to use JOIN instead of multiple subqueries. JOIN can be used to connect multiple tables into one query node, thereby improving query efficiency.

4. Use indexes as much as possible

Using indexes can greatly improve MySQL query efficiency. When designing a database, you should try to add an index to every field in the table to improve query efficiency.

5. Use EXPLAIN to analyze query performance

When optimizing MySQL queries, you can use the EXPLAIN command to view the query plan. In the query plan, MySQL will give each The execution order of query nodes as well as the indexes used in queries, query types and other information can help developers better optimize query nodes.

In short, MySQL query node is an important concept in the MySQL query process. It can help MySQL optimize the execution process of query statements and improve query efficiency. When using MySQL for data analysis and application development, it is important to understand the concept of MySQL query nodes and their role. At the same time, by optimizing MySQL query nodes, it can bring higher performance and better user experience to the application.

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