Thread: array_agg and/or =ANY doesn't appear to be functioning as I expect

Greetings All,
I'm having an issue which is very perplexing. The having clause in a
query doesn't appear to be working as I expect it. Either that or my
understanding of array_agg() is flawed.

I'm using PostgreSQL 10.1, compiled by Visual C++ build 1800, 64-bit.
The table in question looks like:


CREATE TABLE confounded.dataset
(
    seq integer,
    path_seq integer,
    start_vid bigint,
    end_vid bigint,
    node bigint,
    edge bigint,
    cost double precision,
    agg_cost double precision,
    st_length double precision,
    truth boolean
);

The following query returns 3 rows:

with listing as (
      select start_vid, end_vid, array_agg(node order by path_seq)
node_array, array_agg(edge order by path_seq) edge_array
    from confounded.dataset
      group by start_vid,end_vid
    having true =ALL (array_agg(truth))
 )

select * from listing;

The issue is, if I unnest the node_array column from the listing  cte
and do a subselect on confounded.dataset I get back rows where truth =
false.

with listing as (
      select start_vid, end_vid, array_agg(node order by path_seq)
node_array, array_agg(edge order by path_seq) edge_array
    from confounded.dataset
      group by start_vid,end_vid
    having true =ALL (array_agg(truth))
 )
select count(*) from confounded.dataset
where node in (select distinct unnest(node_array) from listing) and
truth = false;

I would expect the above query to return 0 rows.

the dataset can be found at
https://gist.github.com/rhysallister/59239c76e8ec265b81777038bf272879



Rhys
Peace & Love|Live Long & Prosper

Hi Rhys,



Am 2018-01-21 um 02:42 schrieb Rhys A.D. Stewart:
> Greetings All,
> I'm having an issue which is very perplexing. The having clause in a
> query doesn't appear to be working as I expect it. Either that or my
> understanding of array_agg() is flawed.
 >
 > [...]
> 
> with listing as (
>        select start_vid, end_vid, array_agg(node order by path_seq)
> node_array, array_agg(edge order by path_seq) edge_array
>      from confounded.dataset
>        group by start_vid,end_vid
>      having true =ALL (array_agg(truth))
>   )
> select count(*) from confounded.dataset
> where node in (select distinct unnest(node_array) from listing) and
> truth = false;
> 
> I would expect the above query to return 0 rows.


the answer is in your data: "node" is not a UNIQUE field, and there are 
node values with multiple rows.
e.g. node=977 has one row with truth=true and one with truth=false.

So what your second query really does is "select all node values from 
listing for which another entry with truth=false exists in the dataset".

Presuming that "seq" is a primary key [although not declared], you 
probably meant to restrict your query on that.


Best regards,

    -hannes