What does the SQL primary key and index mean?

Primary keys and indexes are key concepts in SQL for optimizing database management and performance. Primary keys force data uniqueness, while indexes improve query performance. The primary key value must be unique, and each table can have up to one primary key; the index values ​​can be repeated, and each table can have multiple indexes. Primary keys and indexes work together to ensure data integrity, prevent duplicate recordings and improve query efficiency.

SQL primary keys and indexes

Primary keys and indexes are two key concepts in SQL for optimizing database management and performance. They help to query and retrieve data quickly and efficiently.

Primary key

A primary key is a column or group of columns that uniquely identifies each row in a table. The purpose is to ensure that there are no duplicate rows in the table.

• The primary key column must contain a unique value.
• Each table can have at most one primary key.
• Primary keys are used to force data integrity and prevent duplicate records from being inserted.

index

An index is a data structure that organizes data in a table into a way to find records faster.

• The index is associated with the table column and stores a pointer to a specific record in the table.
• The index can be a single column index (one column) or a composite index (multiple columns).
• Indexes improve query performance by narrowing the search range.

The difference between primary key and index

• Purpose: Primary keys are used to force data uniqueness, while indexes are used to improve query performance.
• Uniqueness: The primary key value must be unique, and the index value can be repeated.
• Quantity: Each table can have up to one primary key, but can have multiple indexes.

Summarize

Primary keys and indexes are indispensable tools in SQL that work together to ensure data integrity, prevent duplicate records, and improve query efficiency. Understanding the difference between them is important for efficient design and management of databases.

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