"if" condition in SELECT ?

[Margarita Barvinok]

Hello!
I wonder is it possible to write an SQL query to do the following:
There is a table table1 with two fields field1 and field2. Field2 always has some data, field1 - sometimes. I need to select field1, if it's not empty, otherwize - field2.

select (if field1 == NULL then field2 else field1) from table1;

Is this possible in SQL?
I woulld appreciate you help.

Thank you,
-Rita