Please help: How to determine largest of two numbers in a query?

I have a table with the following structure:
    yyyymmdd    int4
    key        char(16)
    value1        int4
    value2        int4

with the following sample data:
    yyyymmdd    key    value1    value2
    19981201    hello    32    16
    19981201    bye    29    64
    19981202    hello    16    20
    19981202    bye    23    13

What I need is to select the greatest between value1 and value2, so the
answer would be:
    yyyymmdd    key    value
    19981201    hello    32
    19981201    bye    64
    19981202    hello    20
    19981202    bye    23

I can do this via ODBC using access by creating a column which is defined as
IF(value1>value2,value1,value2) but that doesn't work in psql.

How can I make this work in psql?

Thanks
Greg