table 1 has a column called ID1
table 2 has two columns called ID1 & ID2
The join would naturally be ID1 = ID1, but my sequence of join needs to be this.
table1.id1 = table2.id1 (but if there is not a match then match on) table1.id1 = table2.id2
is that possible..... to match on one column but if there is no match to try to match to another column?