Creating and modifying primary keys (SQL)

Add primary key, ALTER table [table name: OrderInfo] Add PRIMARY key ([column name: ProductID, UserID ...]) Multiple columns are the combined primary key

Delete primary key, ALTER table [table name: OrderInfo] DROP PRIMARY key

To modify the primary key, first delete the ALTER table [table name: OrderInfo] Drop PRIMARY key statement to delete the existing primary key.

Then execute ALTER table [table name: OrderInfo] Add PRIMARY KEY ([column name: ProductID ...]) Set new primary key

Creating and modifying primary keys (SQL)