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Tag: primary-key

Superkey, candidate key & primary key

Can any kind soul clarify my doubts with a simple example below and identify the superkey, candidate key and primary key? I know there are a lot of posts and websites out there explaining the differences between them. But it looks like all are generic definitions. Example: So from the above example, I can know StudentNumber is a primary key.

Foreign Key Used in Composite Primary Key

Is it possible to use a composite foreign key as a piece of a table’s composite primary key? For instance, let’s say I have two tables: … and then in a second table, I would like to reference the foreign key in the second table’s primary key: Is there any way that I can do that? Yes, it might be

Indexes and multi column primary keys

In a MySQL database I have a table with the following primary key In my application I will also frequently be selecting on item by itself and less frequently on only invoice. I’m assuming I would benefit from indexes on these columns. MySQL does not complain when I define the following: But I don’t see any evidence (using DESCRIBE —

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