# Lookup column - value only once **URL:** \ **Category:** Ask the Community\ **Created:** [October 7, 2022, 7:17am UTC](https://connect.superhuman.com/t/lookup-column-value-only-once/34430 "2022-10-07T07:17:17Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![Iko\_The\_Lost\_Bay](https://yyz1.discourse-cdn.com/coda1/user_avatar/connect.superhuman.com/iko_the_lost_bay/32/28790_2.png) [@Iko\_The\_Lost\_Bay](https://connect.superhuman.com/u/Iko_The_Lost_Bay)\ **Post date:** [October 7, 2022, 7:17am UTC](https://connect.superhuman.com/t/lookup-column-value-only-once/34430/1 "2022-10-07T07:17:17Z")
Hi I’m trying to build something fairly simple but I can’t find a way to set it up. A table with a lookup column where you can’t set the same value twice in two different rows I’ve tried to set up a custom filter in the lookup options, but I can’t understand how to do it Help much appreciated thank you ---
**Author:** ![Quentin\_Morel](https://yyz1.discourse-cdn.com/coda1/user_avatar/connect.superhuman.com/quentin_morel/32/31407_2.png) [@Quentin\_Morel](https://connect.superhuman.com/u/Quentin_Morel)\ **Post date:** [October 7, 2022, 7:33am UTC](https://connect.superhuman.com/t/lookup-column-value-only-once/34430/2 "2022-10-07T07:33:52Z")
Hi mate, my suggestion 🙂 For my example I use a _task_ and a _project_ table, assuming for your example that a project can have only one task 😉 - I assume you have a main table, with a project lookup, and a project table OK? - Start to create a column “Related Task” in **project** table, to check if a task is already linked to the lookup. In my example the formula would be `[Task Test].Filter(Project=thisRow).Count()` ![image](https://global.discourse-cdn.com/coda1/original/3X/1/9/19c17615b6b0e23120ede88ec22795708f57ea67.png) - Then, in the **task** table, for project lookup option, you can make a custom filter, to select only project with related task = 0 ![image](https://global.discourse-cdn.com/coda1/original/3X/9/f/9fcdcc4d35c2a36e10441410c970205467378e87.png) ![image](https://global.discourse-cdn.com/coda1/original/3X/1/6/16fd3b9dd5ea7be39a807096055224b2db720097.png) Is that OK for You ? ---
**Author:** ![Iko\_The\_Lost\_Bay](https://yyz1.discourse-cdn.com/coda1/user_avatar/connect.superhuman.com/iko_the_lost_bay/32/28790_2.png) [@Iko\_The\_Lost\_Bay](https://connect.superhuman.com/u/Iko_The_Lost_Bay)\ **Post date:** [October 7, 2022, 8:31am UTC](https://connect.superhuman.com/t/lookup-column-value-only-once/34430/3 "2022-10-07T08:31:31Z")
That is so clever, works totally! thanks for the quick response! Have a great day! ---
**Author:** ![Quentin\_Morel](https://yyz1.discourse-cdn.com/coda1/user_avatar/connect.superhuman.com/quentin_morel/32/31407_2.png) [@Quentin\_Morel](https://connect.superhuman.com/u/Quentin_Morel)\ **Post date:** [October 7, 2022, 8:32am UTC](https://connect.superhuman.com/t/lookup-column-value-only-once/34430/4 "2022-10-07T08:32:22Z")
Quite simple, but we just need to have the idea ! I let you make this post as **solved** 😉 ! ---
**Author:** ![Iko\_The\_Lost\_Bay](https://yyz1.discourse-cdn.com/coda1/user_avatar/connect.superhuman.com/iko_the_lost_bay/32/28790_2.png) [@Iko\_The\_Lost\_Bay](https://connect.superhuman.com/u/Iko_The_Lost_Bay)\ **Post date:** [October 7, 2022, 8:39am UTC](https://connect.superhuman.com/t/lookup-column-value-only-once/34430/5 "2022-10-07T08:39:52Z")
How do I do that 🙂 ? damn sorry for asking, I’ve looked around for a checkbox, tag, dropdown, whatever and searched the forum, but I can’t find how to do this. ---
**Author:** ![Quentin\_Morel](https://yyz1.discourse-cdn.com/coda1/user_avatar/connect.superhuman.com/quentin_morel/32/31407_2.png) [@Quentin\_Morel](https://connect.superhuman.com/u/Quentin_Morel)\ **Post date:** [October 7, 2022, 8:55am UTC](https://connect.superhuman.com/t/lookup-column-value-only-once/34430/6 "2022-10-07T08:55:34Z")
Ahah that’s indeed a good question 😃 ---
**Author:** ![system](https://yyz1.discourse-cdn.com/coda1/user_avatar/connect.superhuman.com/system/32/24484_2.png) [@system](https://connect.superhuman.com/u/system)\ **Post date:** [October 10, 2022, 8:56am UTC](https://connect.superhuman.com/t/lookup-column-value-only-once/34430/7 "2022-10-10T08:56:21Z")
This topic was automatically closed 3 days after the last reply. New replies are no longer allowed.