In the general case, you can't swap details by updating everything but the primary key because, in the general case, that might involve swapping other candidate keys. (it's the same problem you run into by adding a surrogate key; deferrable constraints work in both cases.). It is a best practice to never update the primary key, and if you find it necessary, you should use a surrogate primary key, which is a key not derived from application data. as a result its value is unrelated to the business logic and never needs to change (and should be invisible to the end user). you can then update and display some other. Sql primary key constraint. the primary key constraint uniquely identifies each record in a table. primary keys must contain unique values, and cannot contain null values. a table can have only one primary key, which may consist of single or multiple fields..
Can anyone tell me if a table in a relational database (such as mysql / sql server) can be without a primary key? for example, i could have table day_temperature, where i register temperature and time.i don't see the reason to have a primary key for such a table.. All the tables can have primary key. but foreign key can only exist in t2 and t3. also every primary key can be a foreign key but every foreign key cannot be a primary key. foreign key can only be created in child tables to maintain referential integrity.. Let's look at an example of how to drop a primary key using the alter table statement in mysql. alter table contacts drop primary key; in this example, we've dropped the primary key on the contacts table. we do not need to specify the name of the primary key as there can only be one on a table..
