Sorry to post this on the list, but I can't find any way of unsubscribing -- I've looked in messages, on the community home pages and on a web search, but all I find is a lot of other subscribers with the same problem.
How do I unsubscribe from this list, please? On 22 May 2015 at 11:46, Nicklas Avén <nicklas.a...@jordogskog.no> wrote: > > > 2015-05-22 skrev Albe Laurenz : > > Nicklas Avén wrote: > >> I was a little surprised by this behavior. > >> Is this what is supposed to happen? > >> > >> This query returns what I want: > >> > >> with > >> a as (select generate_series(1,3) a_val) > >> ,b as (select generate_series(1,2) b_val) > >> ,c as (select generate_series(1,1) c_val) > >> select * from a > >> inner join c on a.a_val=c.c_val > >> full join b on a.a_val=b.b_val > >> ; > >> > >> I get all values from b since it only has a full join and nothing else. > >> > >> But if I change the order in the joining like this: > >> > >> with > >> a as (select generate_series(1,3) a_val) > >> ,b as (select generate_series(1,2) b_val) > >> , c as (select generate_series(1,1) c_val) > >> select * from a > >> full join b on a.a_val=b.b_val > >> inner join c on a.a_val=c.c_val > >> ; > >> > >> also b is limited to only return value 1. > >> > >> I thought that the join was defined by "on a.a_val=c.c_val" > >> and that the relation between b and the rest wasn't affected by that > last inner join. > >> > >> I use PostgreSQL 9.3.6 > >> > >> Is this the expected behavior? > > > >Yes. > > > >In > > > http://www.postgresql.org/docs/current/static/queries-table-expressions.html#QUERIES-JOIN > >you can read: > > > > "In the absence of parentheses, JOIN clauses nest left-to-right." > > > >So the first query will first produce > > > > a_val | c_val > >-------+------- > > 1 | 1 > > > >and the FULL JOIN will add a row for b_val=2 with NULL a_val. > > > >The second query will first produce > > > > a_val | b_val > >-------+------- > > 1 | 1 > > 2 | 2 > > 3 | > > > >an since none but the first row matches a_val=1, you'll get only that row > in the result. > > > >Yours, > >Laurenz Albe > > > Thank you! > > Sorry for not finding it myself, but now I understand why it behaves > like this :-) > > Thanks > > Nicklas > -- Tim Rowe
