Why does mysql add index?

The reasons for adding indexes to mysql: 1. Indexes are data structures used to quickly find and operate data in the database; 2. Indexes can improve query efficiency; 3. Indexes can also optimize table sorting and connection operations. ; 4. Indexes can improve the scalability of the database.

The operating environment of this tutorial: windows10 system, mysql8.0.16 version, DELL G3 computer.

In many relational database management systems (RDBMS), indexes are one of the key factors to improve query performance. For open source databases like MySQL, adding indexes can bring many benefits. This article will discuss why using indexes in MySQL is so important and explain how to use indexes to improve performance.

1. Index is a data structure in the database used to quickly find and operate data. They allow the database to locate matching rows when executing a query without having to scan the entire table. By creating indexes on frequently queried columns, query time and resource consumption can be greatly reduced.

2. Indexes can improve query efficiency. When executing a SELECT statement, MySQL first checks whether an applicable index exists. If there is, the system will use the index to quickly locate the data without scanning the entire table. This can significantly improve query execution speed. In contrast, for a table without an index, MySQL will have to scan the entire table row by row, which may cause query delays and performance degradation.

3. Indexes can also optimize table sorting and connection operations. When executing ORDER BY or GROUP BY statement, MySQL can use the sorting function of the index to sort the results according to the order of the index without sorting the entire result set. For join operations, MySQL can also use indexes to quickly locate matching rows to improve the execution efficiency of the join.

4. Another important aspect is that indexes can improve the scalability of the database. As the amount of data increases, a database without indexes may face the problem of slow queries. The use of appropriate indexes can effectively reduce the time complexity of database queries, maintain good system performance, and adapt to the growing amount of data.

However, indexes are not a panacea, and creating too many indexes without restrictions may lead to performance degradation. Therefore, the costs and benefits of indexing need to be weighed when creating an index. Creating an index takes up disk space, and maintaining the index during insert, update, and delete operations may add additional overhead. To avoid unnecessary index overhead, you need to carefully consider those columns that are most frequently queried when creating indexes.

In addition, for complex queries, sometimes it is more advantageous to create a composite index (that is, an index containing multiple columns) than a single-column index. Query performance can be further improved by creating appropriate composite indexes. However, it should be noted that creating too many composite indexes may result in too many indexes and increase maintenance complexity.

To sum up, adding indexes to MySQL is one of the key steps to improve query performance. Indexes can improve query efficiency, optimize sorting and join operations, and improve database scalability. However, you need to pay attention to the reasonable creation of indexes to avoid performance degradation caused by too many indexes. By using indexes correctly, you can improve the performance of your MySQL database and provide a better user experience .

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