How to set default value in in reference variable in service catalog ?

[shivam kayarkar]

I have one variable in service catalog type is Reference.
I want to set default value (unique value not from record).
Default tab - not working.
So, any other way to set default value it.

[Sandeep Rajput]

@shivam kayarkar put the sys_id of the record in default value field.

[shivam kayarkar]

Hi Sandeep,
Thank for suggestion.
But my value is Unique (Random) value.
It is not record so that don't have any sys_id.

[Sandeep Rajput]

@shivam kayarkar You can't set any random value as default value on a reference field. It has to be a sys_id from the reference table. Otherwise the default value will not be set on the reference field.

[shivam kayarkar]

ok.

If I set it from table, then the variable turns mandatory to non-mandatory.
But I want variable mandatory only, unless another record not selected. 
is it possible to do.