I have the following problem:
Assuming the table TEST as follows:
ID NAME
-----------------
1 Alex
2 Oliver
1 Thomas
2 Fenella
SELECT DISTINCT ON id id, name FROM test;
produces:
ID NAME
-----------------
1 Alex
2 Oliver
SELECT DISTINCT ON id, name FROM test ORDER BY name;
produces:
ID NAME
-----------------
1 Alex
2 Fenella
1 Thomas
I would have expected only two rows in both queries. I don't care which
names actually appear in the output as long as they are sorted, but
there should no longer be duplicate id's.
If the table is as follows:
ID NAME
-----------------
2 Oliver
2 Alex
1 Thomas
1 Fenella
SELECT DISTINCT ON id id, name FROM test;
produces:
ID NAME
-----------------
1 Thomas
2 Oliver
SELECT DISTINCT ON id, name FROM test ORDER BY name;
produces:
ID NAME
-----------------
2 Alex
1 Fenella
2 Oliver
1 Thomas
What seems to happen is that from the sorted table, duplicate id's are
eliminated only if they are grouped. If there is no explicit sorting I
assume the DISTINCT performs an implicit sorting on id and then
eliminates records correctly. Is that the correct behaviour? Is there
another (simple) way of getting the results I want?
I am still using version 6.3
tm
--
Thomas Metz
GSF - National Research Center for Environment and Health
Institute of Mammalian Genetics
