How to Make an Existing MySQL Field Unique?

Making an Existing Field Unique in MySQL

In some instances, an existing table may require a field to be uniquely indexed. This ensures that each row in the table has a distinct value for that field, preventing duplicate entries.

How to Implement a Unique Constraint

To make a field unique, you can use the following SQL statement:

ALTER IGNORE TABLE [mytbl_name] ADD UNIQUE ([column_name]);

MySQL 5.7.4 and Later

For MySQL versions 5.7.4 and later, the IGNORE clause has been removed. As such, the syntax for adding a unique constraint becomes:

ALTER TABLE [mytbl_name] ADD UNIQUE ([column_name]);

Important Note

Before adding a unique constraint, it's crucial to remove any duplicate entries that may exist in the table. The IGNORE clause, which was previously used to ignore duplicate rows, is no longer supported.

Reference:

For more information on creating unique indexes, refer to the official MySQL documentation.

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