AW: Full outer join to show differences

David,

when joining 2 tables you can only compare the key values:

Select a.*, b.*

From Table1 a full outer join Table2 b on a.Key1 = b.Key1 and a.Key2 =

b.Key2 ...

Assumed we have the following tables
Table1:
KeyId Data
1 'ABC'
2 'XXX'
3 'YYY'

Table2:
2 'XXX'
3 'ABC'
4 'ZZZ'

The full outer join will return:
1 ABC NULL NULL
2 XXX 2 XXX
3 YYY 3 ABC
NULL NULL 4 ZZZ

What you know is, that KeyId 2 and 3 are in both tables, but only the rows
with the keyId 2 is identical. For keyId the data are different.

When using EXCEPT and UNION the SQL Statements are merged.
EXECPT returns all rows that are in TableA and not in TableB
UNION merges the rows, but removes duplicates.

When executing the following SQL statement:
(Select * from Table1 Except Select From Table2) Union (Select * From Table2
Except Select * From Table1)

You'll get the following result:
1 ABC
3 YYY
3 ABC
4 ZZZ

The rows with the keyId 2 are not shown because they are identical, but the
rows with the KeyId 3 are listed, because the data is different.


Mit freundlichen Grüßen / Best regards

Birgitta Hauser

"Shoot for the moon, even if you miss, you'll land among the stars." (Les
Brown)
"If you think education is expensive, try ignorance." (Derek Bok)
"What is worse than training your staff and losing them? Not training them
and keeping them!"


-----Ursprüngliche Nachricht-----
Von: midrange-l-bounces@xxxxxxxxxxxx
[mailto:midrange-l-bounces@xxxxxxxxxxxx] Im Auftrag von David FOXWELL
Gesendet: Thursday, 10. March 2011 16:09
An: Midrange Systems Technical Discussion
Betreff: RE: Full outer join to show differences


Birgitta do you mean exception join? I ask as you say to merge and not to
join!

Joe, I was already trying IFNULL () but I get an error message.
Charles, thanks I was also trying ISNULL()??? and also getting an error
message!

-----Message d'origine-----
De : midrange-l-bounces@xxxxxxxxxxxx
[mailto:midrange-l-bounces@xxxxxxxxxxxx] De la part de Birgitta Hauser
Envoyé : jeudi 10 mars 2011 15:20
À : 'Midrange Systems Technical Discussion'
Objet : AW: Full outer join to show differences

Hi,

you only want to see the rows that are either different or do
not exist?

IMHO joining is the wrong way, what you need is merging.

The following statement returns all rows that are not identical:

( Select * from Table1
Except
Select * from Table2)
Union
( Select * from Table2
Except
Select * from Table1)


Mit freundlichen Grüßen / Best regards

Birgitta Hauser

"Shoot for the moon, even if you miss, you'll land among the
stars." (Les
Brown)
"If you think education is expensive, try ignorance." (Derek
Bok) "What is worse than training your staff and losing them?
Not training them and keeping them!"


-----Ursprüngliche Nachricht-----
Von: midrange-l-bounces@xxxxxxxxxxxx
[mailto:midrange-l-bounces@xxxxxxxxxxxx] Im Auftrag von David FOXWELL
Gesendet: Thursday, 10. March 2011 14:39
An: Midrange Systems Technical Discussion
Betreff: Full outer join to show differences

Hi,

I'm comparing 2 tables after a test with a full outer join ie

select * from before b full outer join after a on b.id=a.id

But I only want to see the data that's different in the after
table or not there at all, ie null in that select.

So I add
where a.data<>b.data

This now excludes the missing after lines.

So I need something like

select * from before b full outer join after a on b.id=a.id
where a.data<>b.data or b.data= null

How do I get those null rows?

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