How to Fix \"Error 1062 (23000): Duplicate entry\" When Adding a Primary Key in MySQL?

How to Append a Primary Key to a MySQL Table

When attempting to add a primary key to a MySQL table, you may encounter errors similar to the one described in the question. This error occurs if you use the PRIMARY keyword instead of PRIMARY KEY.

To correctly add a primary key to a table, follow these steps:

1. Add the Column:

   • Add a new column to your table using the ALTER TABLE statement. Specify the column name, data type, and other attributes.

   <code class="sql">ALTER TABLE goods ADD COLUMN `id` INT(10) UNSIGNED;</code>

2. Specify the Primary Key:

   • Once you have added the new column, you can specify it as the primary key using the ALTER TABLE statement again.

   <code class="sql">ALTER TABLE goods ADD PRIMARY KEY (id);</code>

As an example, the corrected query that the user was attempting to use would be:

<code class="sql">ALTER TABLE goods ADD COLUMN `id` INT(10) UNSIGNED PRIMARY KEY AUTO_INCREMENT;</code>

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