How to achieve unique in mysql

MySQL's UNIQUE constraint enforces uniqueness on a specific column or column group by creating a B-Tree index, ensuring that each row has a unique value and allowing null values ​​as distinct values.

Uniqueness implementation of UNIQUE constraint in MySQL

UNIQUE constraint is a database constraint that enforces the Each row of has a unique value on a specific column or set of columns. This means that no duplicate values ​​can occur in a column or column group subject to a UNIQUE constraint.

Implementation method:

MySQL uses B-Tree index to implement UNIQUE constraints. When you create a UNIQUE constraint on a table, MySQL creates a B-Tree index on the constrained column. B-Tree index is an efficient data structure that can quickly find and compare values.

MySQL checks for UNIQUE constraints when inserting data into a table. If the inserted data matches existing data on the indexed column, an error is raised and the insert is blocked.

Additional notes:

• The UNIQUE constraint allows null values, but null values ​​in different rows on the same column are considered different values.
• UNIQUE constraints can be defined across multiple columns, in which case the values ​​for the combination of these columns must be unique.
• If you update a value on a column with a UNIQUE constraint, and the new value contradicts the existing value, the update will also be rejected.
• The UNIQUE constraint is more efficient than the PRIMARY KEY constraint because it allows null values ​​and can be defined on multiple columns.
• PRIMARY KEY constraints implicitly include UNIQUE constraints, which means that PRIMARY KEY columns are always unique.

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