Access 2002

I want to merge 2 tables they both have the same field names and same data except for some rows have data that the other table does not have. I want to extract the data from one table and insert it where the data in the other table where it is missing and if it is the same leave. For example:

Table1 Duns# Table 2 Duns#
1 1
1
1
Take the data say from Table 2 when the data in table one is missing and if it is the same leave. I was thinking that an SQL IF and or a CASE statement might work but unsure how to compile the two together along with SELECT, unless someone has a better idea. Thanks.