Restrict duplicate entries based on two conditions

[MitchLags]

Hi,
I know this has been covered on multiple threads but I can not figure out a method to adapt to my situation. 

I have a form users can fill in appsheet, In short its a Name selection & Topic selection followed up with a signature. I want to stop users from being able to enter the same name and topic more than once. for example, Jeff can be signed off on 10 different topics but all topics have to be unique and he should not be able to submit the same one twice. 

I need a formula which will display only outstanding topics(Toolboxtalks) based on the name entered. I feel like it should be so simple, if this would have been in sheets i'd have no issue but expressions are a different language here.  

Thank you.

[Markus_Malessa · Accepted solution]

Proposed Valid:

ISBLANK(SELECT(TableName[id], AND([_THISROW] <> [id], [_THISROW].[Name] = [Name], [_THISROW].[Toolboxtalk] = [Toolboxtalk]))

This should check your existing data only for a match and at the same time prevent an error to crop up if you have to resave an existing row in the table.

[MitchLags]

Thank you Markus
Apologies, Im lacking some knowledge here. What would be the [id] ? Is it my Key column? 

[Markus_Malessa]

Yes it would be the key column

[MitchLags]

Perfecto, this works however it has removed the dropdown.

Previously I had 'Toolbox talks. [Toolboxtalk] ' in the valid if section to generate a drop down, using the Ref option returns numbers rather than text to my spreadsheet. 

Do you know of away to use this Valid if formula and still use a drop down? 

[Markus_Malessa]

Yes, whatever you had in your Valid If expression before, move that to the Suggested Values section instead.

[MitchLags]

Works perfect. Thank you Markus 😃🤝