1. Introduction
SharePoint Cascaded Lookup greatly enhances the default SharePoint lookup and even further reduces waiting time as lookup results are filtered according to the parameters you set. Column relationship between parent and child columns are built, data selected inparent field will determine the options presented in the child field.
2. Related Concept
In order to maximize the power of your Cascaded Lookup, you must set up several things:
Source List - list where Cascaded Lookup will refer for information. The Source List can be in any site in the current site collection.
Source Column - located in the Source List, contains data for your dropdown menu.
Filter Column - also located in the Source List, is used to filter out irrelevant data from the Source Column and is also available as dropdown menu.
Parent Column - located in the target list (the list where you want to add looked up information)
3. Configuration
Sample scenario:
A project team needs to make a development plan based on product features.
We have the following list:
Products - list all of products with different category
Product Release History - list all of released product with different version and release date
Project Tasks - list all of tasks of project team recorded
Sprint Backlog - list project plan of product development of project team
And now we need add a cascaded lookup column "Related Tasks" in Sprint Backlog list to join related project tasks.
The following is the detail process:
Go to Sprint Backlog list, click "Create Column".

3.1 General Settings
Enter column name "Related Tasks" and select Cascaded Lookup as column type
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Specify Project Tasks as the source lookup list and Title as source column, and specify which column(s) as additional column(s)

3.2 Filter Settings
3.2.1 Build single or multiple parent-child relationships by adding one or more filters
In this scenario, we can specify Product column and Product version column as the parent column of the Related Tasks column in Sprint Backlog list, and specify the associated column in source list.

By this way, the lookup items of child column (Related Tasks) will be filtered by parent columns (Product and Product Version). The following is the result:

3.2.2 Filter lookup items by multiple columns
Add one or more columns from source lookup list as filter column, and do not specify the parent column in current list. In this scenario, we can specify Priority column and Task Status column as filter column in the source lookup list.

By this way, the lookup items of Related Tasks column will be filtered by Priority column and Task Status column in source lookup list. The following is the result:

3.3 Advanced Settings

Create New Item- enable adding new item in the source lookup list by the"Create new item…" link
Show Empty- enable displaying empty field when no items match filter criteria
Do not repeat identical values- items with same name will not be duplicated
3.4 Convert Column

A popup window will prompt you to choose which lookup column to convert

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