What does key mean in mysql

Keys in MySQL are special indexes used to quickly find data. They include primary keys (unique identifiers), unique keys (unique but allow null values), composite keys (consisting of multiple columns), foreign keys (linked to another table), and index keys (to improve the performance of a specific query). Keys speed data retrieval, enforce data integrity, improve performance, and reduce redundancy. When choosing the appropriate key type, you should consider data uniqueness, query mode, table size, and data integrity requirements.

Keys in MySQL

In MySQL, a key is a special type of index used to quickly find and retrieve data. It is a data structure that maps specific columns or combinations of columns to their position in a row in a table.

Types of keys

MySQL supports multiple types of keys:

• Primary key (PRIMARY KEY): uniquely identifies each row in the table column or column combination.
• Unique key (UNIQUE): A column or column combination that uniquely identifies each row in the table, but null values ​​are allowed.
• COMPOUND KEY: A key composed of multiple columns, each of which must be unique and non-empty.
• Foreign key (FOREIGN KEY): A column or column combination that points to the primary key in another table, used to establish relationships between tables.
• INDEX KEY: A secondary key created on a column or combination of columns to improve the performance of a specific query.

The role of keys

Keys play a vital role in MySQL, they:

• Speed ​​up data retrieval:By looking up on a key, MySQL can directly access a specific row without scanning the entire table.
• Enforce data integrity: The primary key ensures that each row in the table has a unique identifier. Foreign keys ensure data consistency between related tables.
• Improve performance: Optimized keys can greatly improve query speed, especially for large databases.
• Reduce data redundancy: By setting columns as keys, you can reduce the storage of duplicate data.

Choose the appropriate key type

Choosing the correct key type is very important for optimizing MySQL performance. Consider the following factors:

• Uniqueness: If the data must be unique, choose a primary key or a unique key.
• Query mode: Determine which columns or column combinations are frequently used in queries.
• Table size: For larger tables, composite keys or index keys can provide better performance.
• Data integrity: If you need to ensure data consistency, please use foreign keys.

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