What is key in mysql

Key in MySQL is an index used to optimize data retrieval. It organizes data rows by specified columns, allowing MySQL to quickly find rows that match query criteria, thereby reducing retrieval time. MySQL supports multiple key types, including primary keys, unique keys, index keys, and full-text indexes. Choosing the right key is critical and requires consideration of factors such as query pattern, data distribution, and update frequency. By optimizing key usage, data retrieval speed in MySQL can be significantly improved.

#What is key

key in MySQL?

Key is a special type of index in MySQL, used to improve the speed of data retrieval. It is essentially a sorted list containing rows of data from a table, organized by specified columns.

The role of key

When MySQL needs to find data, it will use key to quickly locate rows that match the query conditions without scanning the entire table. This greatly reduces retrieval time, especially when the table contains large amounts of data.

Key types

MySQL supports multiple key types, including:

• Primary Key: uniquely identifies each key in the table A row of columns.
• Unique Key: A column with no duplicate values ​​in the table.
• Index Key: Uniqueness is not guaranteed, but it can speed up the query.
• Full-Text Index: Used for full-text search, which can retrieve lines containing specified words in the text field.

Creation of key

You can create a key in the following ways:

• Specify PRIMARY KEY when creating the table or UNIQUE constraints.
• Use the CREATE INDEX statement to create a non-unique index.

Selection of key

Choosing the appropriate key is crucial because it affects query performance. Here are some considerations:

• Query mode: Select the key based on the most common query mode for the table.
• Data distribution: Consider the distribution of data to select the key that best distinguishes rows.
• Update frequency: If the table is updated frequently, please avoid using keys with high update costs (such as primary keys).

By carefully considering these factors, you can optimize the use of keys, thereby significantly improving the speed of data retrieval in MySQL.

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