RE: Suggestion with SQL query

From: Donald Whittaker

I believe you are _asking_ for one thing and
showing an _example_ of another.
Going by the example, the first returned row shows
data from field 'value' in table T2. The second shows
data from field 'value' in table T1 as there is no
matching row in table T2. To do that, you could use
the COALESCE function:
...select id, type, COALESCE(T2.value, T1.value)...

Yes, Don is exactly right here, and here's why: what you really are saying
is that the value field in T2, if it exists, overrides the value field in
T1. That being the case, you JOIN the two files using LEFT OUTER JOIN; this
will return a NULL value from T2 if no matching record exists. Then, you
use the COALESCE function, which will return the first non-NULL value in a
list.

Thus:

SELECT t1.id, t1.type, COALESCE(t2.value, t1.value)
FROM t1 LEFT OUTER JOIN t2 ON t1.id = t2.id and t1.type = t2.type

That ought to do the trick. Basically, if there is a row in T2, t2.value
will be used. Otherwise, t2.value will be NULL and t1.value will be used.

Joe