N/ui/serverWidget Module
Sublist.updateUniqueFieldId()
Method Description: Indicates a field that must have unique values across the rows in the sublist. This method is available on inlineeditor and editor sublists only.
Returns: serverWidget.Sublist object
Supported Script Types: SuiteScript 2.0 Suitelet Script Type and SuiteScript 2.0 User Event Script Type (beforeLoad(scriptContext))
Governance: None
Module: N/ui/serverWidget Module
Since: 2015.2
Search NetSuite - https://system.netsuite.com/app/help/helpcenter.nl?search=Sublist.updateUniqueFieldId(options)

// Code Example 1

//Add additional code

//...

var form = serverWidget.createForm({

    title : 'Simple Form'

});

var sublist = form.addSublist({

    id : 'sublist',

    type : serverWidget.SublistType.INLINEEDITOR,

    label : 'Inline Editor Sublist'

});

sublist.addField({

    id : 'fieldid',

    type : serverWidget.FieldType.DATE,

    label : 'Date'

         });

sublist.updateUniqueFieldId({

    id : 'fieldid'

})

//...

//Add additional code



//SOURCE: https://system.netsuite.com/app/help/helpcenter.nl?fid=section_46467834472.html