using sql to update record individually

I have 2 table one is items and the other is invoicedetails

recently I have added an additional field to the invoicedetails,
which a UNIT2 and CONVERSION. This 2 fields exists on the items
table. Since the field UNIT2 and conversion is just recently added, I
want to fill those null fields with values from the items table.

Is there a sql statement to do this job? But not using stored
procedures.

thanks.