Re: [sqr-users] DISTINCT problem

["George Jansen" <GJANSEN@aflcio.org>]

This came in somewhere in Oracle 8.1. It makes sense, if you think about
it: Suppose you have a table X

A          B
---       ----
1          2
1          3
2          2
2          3

SELECT A FROM X ORDER BY B

is not a problem. But if we

SELECT DISTINCT A FROM X ORDER BY B

and there are multiple values of B for some A, what does that ordering
mean? I guess the SQL engine could figure out whether you have a
functional dependency, but throw in a function or two and it could get
tricky. An example of the error follows:



SQL> create table a (b number, c number);

Table created.

SQL> select b from a order by c;

no rows selected

SQL> c/b/distinct b
  1* select distinct b from a order by c
SQL> /
select distinct b from a order by c
                                  *
ERROR at line 1:
ORA-01791: not a SELECTed expression



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