Dataset column lookups

I’ve two datasets with list of urls in each, just one column without any column names. I want to get a random row from dataset1 if a condition matches else get a random row from dataset2. I’ve tried the following formula

if field("IsDataset1") == 'yes' then from_dataset("dataset1") else from_dataset("dataset2") end

i get the following error

error: wrong number of arguments (1 for 3 )

however, i don’t understand what possible values i could give for columnName and join_criteria as both datasets are single column and has no header.