Salesforce provides the ability to mark fields as required and as unique. These options work exactly as you would expect them to work. If you try to submit a record with an empty required field, you get an error.
If you try to submit a unique field with a duplicate value, you get an error.
So, none of this is really a surprise. This is how Salesforce explains these features will work. Typically, this functionality is used together to enforce a user to enter a value into a unique field. However, there may be a time where we want just a single instance of the object with the unique field set to null. If the field isn’t required, we should be able to have a single instance of null and then any duplicates will error out. Considering Salesforce describes the unique feature as “preventing duplicate field values”, it is reasonable to expect a second null instance to error out. However, that is wrong!
While in every other instance, null == null or '' == '' would return true, in the scenario where you have a field marked as unique but not did mark it as required, you can save multiple instances of that object without ever specifying the unique field. Like below:
With my unique field set up as:
I can progress through the following screen twice by just pressing Save:
This results in:
As you can see, a unique field is only considered unique if you enter a value. Two empty strings do not fire off the validation. This can be a problem and something that should be considered when creating a truly unique field.
