SharePoint Lookup field, what is it?

Question

SharePoint Lookup field, what is it?

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Answer 1

It is a type of field used to indicate that the possible values of a column in a list must be taken from the elements of another list. For example, if you have a list of users, and one column of this list is the country, you can create a lookup field pointing to another list "countries" which contains the possible values to select.

Answer 2

If you think in terms of relational databases, a lookup field is a foreign key: you only store a reference to the related item, not its value.

For instance, you have a list of meeting rooms. You can create a meeting calendar by creating a new calendar list with a lookup to the "Meeting rooms" list. Hence, when organizing a meeting, you will be able to pick a room from the list of meeting rooms entered previously.

A "Lookup" differs from "Choice" field as you may alter the source item and the referencing item is updated automatically. For instance, you change the name of a meeting room - all meetings booked for that room will show the new title automatically.