SharePoint Cascaded Lookup is a powerful look-up tool that greatly enhances the lookup functionality already native to SharePoint. It quickly cross-references existing data from a list or site from any site collection (it works across site collections) and then applies a combination of filters to reduce the number of options presented in the dropdown menu of your lookup field. To use it, you set a combination of filters available in both the source list (the list you are looking up from) and the target list (the list where you want to add looked-up information) to ensure that only applicable values are displayed as choices in the dropdown list.

SharePoint Cascaded Lookup creates relationships between columns in the same list: you build a parent-child relationship between a set of columns so that the value you choose in the parent column determines the options presented in the child column.

How Does It Work?

In order to take full advantage of the functionality of Cascaded Lookup, you need to establish several things:

* The Source List, which is the list from which Cascaded Lookup will look up information. The Source list can be in any site collection.
* The Source Column, located in the Source List, that contains all of the possible values for your drop-down menu.
* The Filter Column, also located in the Source List, which is used to filter out irrelevant data from the Source Column so that only values that fit your filter criteria will be possible as choices.
* The Parent Column, located in the target list (the list where you want to add looked up information).

Setting up a Cascaded Lookup column

Once you have set up your filter columns, Cascaded Lookup will automatically filter according to your parameters:

* You select a value from the Parent column.
* SharePoint takes this value and compares it to the values located in the Filter Column (in the Source List).
* SharePoint instantly builds a list of possible choices by listing the Source Column values for rows with Filter Columns that match the value of the Parent Column. These results are then listed in the drop-down menu all non-matching values have been filtered out, so they do not appear as possible choices.

For each item you create, Cascaded Lookup will apply the filter criteria you specified when you set up the column:

An example of a cascading series of parent-child columns that filter the options presented in the final drop-down menu. The filter columns automatically remove inapplicable values

SharePoint Cascaded Lookup is an invaluable lookup tool, saving you time by reducing the options presented in the drop-down list, and eliminating the possibility for error as a result of incompatible values.