One of the column types used when creating new columns for a list or library is the Choice (menu to choose from)
type. This is OK to use when there is a short list that will never change, but if the list is long or something that's going to changed and be updated over time, you'll need a better solution. That's where a lookup list comes in.
A look up list is a custom list that holds all the choices you would want for a dropdown list. The trick is to point to the custom list from another list or library when the list is needed. Examples include the days of the week (7), months of the year (12), states in union (50), planets in the solar system (8 or 9, depending upon who you talk to).
Follow these steps to create your lookup table and link it to another list:
- Create a lookup list
- Site Actions -> Create
- Custom Lists: Custom List
- Configure New screen
- Name: Lookup_DaysOfWeek
- Description: Days of the week
- Display on Quick Launch?: No
- Click Create button
- Use the New button or Datasheet view to enter the names of the week in the title column
- Use the lookup list in a library
- Open an existing library or create one (that needs days of the week as a column)
- Settings -> Create Column
- Column configuration screen
- Column name: Day of the Week
- The type of information in this column is: Lookup (information already on this site)
- Description: Choose a day of the week
- Require that this column contains information: Yes
- Get information from: Lookup_DaysOfTheWeek
- In this column: Title
- Click OK button
When you create a new item in the library, you will now have a dropdown list available to you that contains the days of the week. This is great when you have to use the same lookup list in multiple places on your site. Create it once and then point to it as needed.
Moral of the story? If your list is longer than three items and has the potential for reuse, create a lookup list and relax.