what is mysql index

The index in MySQL means index. It is a data structure used to speed up the query of database tables. The index can be compared to the catalog of a book, which stores the values ​​of specific columns in the table and the corresponding rows. location, enabling the database to locate and access data faster. The function of the index is to improve query efficiency. Without an index, the database needs to scan the entire table row by row to find matching data. This method will be very time-consuming in large tables. With an index, the database can The required data rows are quickly located in the order, which greatly improves the query speed.

The index in MySQL is a data structure used to speed up querying of database tables. Indexes can be compared to the table of contents of a book. They store the values ​​​​of specific columns in the table and the corresponding row positions, allowing the database to locate and access data faster.

The function of index is to improve query efficiency. Without indexes, the database needs to scan the entire table row by row to find matching data, which can be very time-consuming in large tables. With the index, the database can quickly locate the required data rows according to the order of the index, thus greatly improving the query speed.

Indexes in MySQL can be divided into primary key indexes and non-primary key indexes. The primary key index is a unique index that is used to identify each row of data in the table, ensuring that each row has a unique identity. Non-primary key indexes are indexes created on other columns in the table. Multiple non-primary key indexes can be created according to different query requirements.

You can use the CREATE INDEX statement to create an index. The syntax is as follows:

CREATE [UNIQUE] INDEX index_name
ON table_name (column1, column2, ...);

Among them, index_name is the name of the index, table_name is the name of the table to create the index, column1, column2, etc. are to create the index. Column name. If you use the UNIQUE keyword, it means that the created index is a unique index, that is, the value of the index column is guaranteed to be unique.

In addition to using the CREATE INDEX statement to create an index, you can also use the ALTER TABLE statement to add an index. The syntax is as follows:

ALTER TABLE table_name
ADD [UNIQUE] INDEX index_name (column1, column2, ...);

Using indexes can speed up the query, but it will also increase the data storage space and The time of the write operation. Therefore, when creating an index, you need to balance query efficiency and storage space requirements to avoid performance degradation caused by excessive use of indexes.

In addition, when updating, inserting and deleting operations on the table, the index also needs to be maintained accordingly. Therefore, when designing a database, the selection and use of indexes need to be considered to improve the overall performance of the database.

In short, index is an important concept in MySQL, which can improve the query efficiency of the database. By properly creating and using indexes, you can speed up queries and improve the response performance of the system. But at the same time, you also need to pay attention to the storage space and maintenance costs of the index to avoid performance degradation caused by overuse of the index.

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