Re: 3 value logic. Why is SQL so special?

David Portas wrote:
> Chris Lim wrote:

> As Bob already stated, an "outer join" is not really a join. It is
> SQL's syntax shortcut for a UNION. Obviously the answer to your
> question depends on the desired result from such a UNION. The user can
> contrive a query to return whatever values are deemed suitable.
A UNION equivalent an LEFT OUTER JOIN BULLSHIT!!!. A LEFT OUTER JOIN is just SQL miserable way to force a presentation inspired perspective into design issues that should be regulated by normalization to preserve integrity. The proof is that you can do a UNION using 2 relations but using LEFT OUTER JOIN when dealing with relations has no meaning. Consider 2 tables table1(id1, key1) and table2(id2, key2)

Table1

1, A
2, B
3, C

Table2
8, A
10, C

Table1 LEFT OUTER JOIN Table2 on key1 = key2 produces the following view

1, A, 8, A
2, B, NULL, NULL
3, C, 10, C

Table1 UNION Table2 produces

1, A
2, B
3, C
8, A

So basically stating that UNION = LEFT OUTER JOIN is stating that

1, A, 8, A
2, B, NULL, NULL
3, C, 10, C

1, A
2, B
3, C
8, A

?... Received on Sat Sep 16 2006 - 19:22:54 CEST