user sqlload load data to mutiple tables

user sqlload load data to mutiple tables

now we are tring to load data from txt file to two diffierent to tables in the database.the key part to diffierciate different date is by recongenizing whether CLOUMN A is null or not.

when A IS NULL to TABLE1

when B IS NOT NULL TO TABLE2

But problem is we can not use clause like 'WHEN A IS NULL' in control file.Are there any other ideas?eagering for your help,thank you !