A ____ key can be any column or smallest combination of columns that can qualify as a unique key in a database, and there can be multiple such keys in one table. Each of these can qualify, but only one can be chosen as a ____ key. The ones that are not chosen are called ____ keys. However, when the smallest group of columns is chosen, then it is called the ____ key. Sometimes, if no columns can be used to ensure uniqueness, or a composite key is inappropriate, then it is normal to introduce a new column as a ____ key. When the primary key from one table appears in another table to link them together, it is known as a ____ key. They are used to specify that this record in this table is related to that record in that table.

Database keys

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