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The syntax for creating a unique index in MySQL: CREATE UNIQUE INDEX index_name ON table_name (column_name); This syntax can be used to create a unique index to ensure that the values of specific columns in the table are unique and prevent duplication. Unique indexes help ensure data integrity and improve query performance, but they affect the performance of insert and update operations and consume resources during creation.
How to create a unique index in MySQL
Syntax for creating a unique index:
<code>CREATE UNIQUE INDEX index_name ON table_name (column_name);</code>
Example:
<code>CREATE UNIQUE INDEX idx_username ON users (username);</code>
Effect:
The unique index created will ensure that the users
table The values in the username
column are unique. That is, no two rows can have the same username
value.
Benefits of unique index:
Note:
NOT NULL
constraint. The above is the detailed content of How to write unique in mysql. For more information, please follow other related articles on the PHP Chinese website!