Compare tables, find rows that are "different"

Question

A common problem in replication/query-extract-load scenarios is comparing two sets of data, and finding the rows that have changed or are different. A clean solution to this is less obvious than it sounds, because "different" can involve nulls (love them!/hate them!).
Consider two structurally identical tables with all data linked by a common PK:
Snapshot A Snapshot B
PK First Last State PK First Last State
1 Bob Smith AZ 1 Bob Smith AZ
2 Louise Jones FL 2 Louise Brown FL
3 Joe Jones NULL 3 Joe Jones CA
4 Joe NULL GA 4 Joe Celko NULL
5 Phill NULL AL 5 Phill NULL AL
If we are interested in tracking or processing any changes in our data, we would agree that only Rows 1 and 5 are "the same" in both sets A & B.
Because of null logic, this sql only gets me row 2 (besides being syntactically miserable with a wide table) :
select A.PK from A inner join B on A.PK = B.PK
where (A.First <> B.First) OR (A.Last <> B.Last) OR (A.State <> B.State);
So how can I select rows 2, 3, and 4? (Extra credit for for a query I can type in less than two minutes with a pair of tables that have 42 columns)
Thanks much,
Steve Pence
DBA
Wycliffe Bible Translators
Orlando
[email protected]

Answer 1

Sorry, my post got mangled by the white space deleterer...
A common problem in replication/query-extract-load scenarios is comparing two sets of data, and finding the rows that have changed or are different. A clean solution to this is less obvious than it sounds, because "different" can involve nulls (love them!/hate them!).
Consider two structurally identical tables with all data linked by a common PK:
Snapshot A
PK First Last State
1 Bob Smith AZ
2 Louise Jones FL
3 Joe Jones NULL
4 Joe NULL GA
5 Phill NULL AL
Snapshot B
PK First Last State
1 Bob Smith AZ
2 Louise Brown FL
3 Joe Jones CA
4 Joe Celko NULL
5 Phill NULL AL
If we are interested in tracking or processing any changes in our data, we would agree that only Rows 1 and 5 are "the same" in both sets A & B.
Because of null logic, this sql only gets me row 2 (besides being syntactically miserable with a wide table) :
select A.PK from A inner join B on A.PK = B.PK
where (A.First <> B.First) OR (A.Last <> B.Last) OR (A.State <> B.State);
So how can I select rows 2, 3, and 4? (Extra credit for a query I can type in less than two minutes with a pair of tables that have 42 columns)
Thanks much,
Steve Pence
DBA
Wycliffe Bible Translators
Orlando
[email protected]