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Databases Querying Relational Databases Database Keys Unique Keys

Ololo Olololo
PLUS
Ololo Olololo
Courses Plus Student 1,816 Points
Posted by Ololo Olololo
Ololo Olololo
Courses Plus Student 1,816 Points

Did the lecturer forget to add that Unique key can be set on a combination of columns: email AND credit_card_number?

?

1 Answer

Steven Parker
Steven Parker
231,275 Points
Steven Parker
Steven Parker
231,275 Points

:point_right: Unique keys can be set on multiple columns.

You can have more than one unique key column in a table, and a unique key can be composed of more than one column.

As an example of the latter, imagine you had a table of items of different types and each type had serial numbers. The numbers are only unique for a certain type. So neither the type nor the serial number could be used as unique keys in themselves, but a key composed of both a type and serial number would be guaranteed unique.

Hmm, it looks like your question changed after I answered. So if you're just asking why the concept was not introduced in the video, perhaps it will be presented later or in a more advanced course.