How do I add a primary key to a MySQL table and avoid common errors?

Adding a Primary Key to a MySQL Table

Adding a primary key to a MySQL table can be accomplished through specific syntax. However, some users may encounter errors when attempting this operation.

How to Add a Primary Key

To add a primary key to a table, use this syntax:

ALTER TABLE [table_name] ADD PRIMARY KEY ([column_name]);

For example, to add a primary key to the goods table with a column named id:

ALTER TABLE goods ADD PRIMARY KEY (id);

Troubleshooting Common Error

One common error that may occur is when attempting to create a primary key while adding the column. The following syntax will not work:

ALTER TABLE goods ADD COLUMN `id` INT(10) UNSIGNED PRIMARY AUTO_INCREMENT;

To resolve this issue, specify PRIMARY KEY instead of just PRIMARY. The correct syntax is:

ALTER TABLE goods ADD COLUMN `id` INT(10) UNSIGNED PRIMARY KEY AUTO_INCREMENT;

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