Thread

1. How to eliminate extra "NOT EXISTS"-query here?

   Andreas Joseph Krogh <andreas@visena.com> — 2023-11-25T13:26:56Z

   
   Hi, I'm testing if some dataset contains an array of elements and want to 
   return all “not containing the specified array”, including entries in master 
   table not being referenced.
   
   
   
   I have the following schema:
   
   drop table if exists stuff;
   drop table if exists test;
   CREATE TABLE test(
   id varchar primary key
   );
   
   create table stuff(
   id serial primary key,
   test_id varchar NOT NULL REFERENCES test(id),
   v varchar not null,
   unique (test_id, v)
   );
   
   INSERT INTO test(id) values ('a');
   INSERT INTO test(id) values ('b');
   INSERT INTO test(id) values ('c');
   INSERT INTO test(id) values ('d');
   
   INSERT INTO stuff(test_id, v)
   values ('a', 'x')
   ;
   
   INSERT INTO stuff(test_id, v)
   values ('b', 'x')
    , ('b', 'y')
   ;
   
   INSERT INTO stuff(test_id, v)
   values ('c', 'x')
    , ('c', 'y')
    , ('c', 'z')
   ;
   
   select * from test t
   WHERE NOT ARRAY['x']::varchar[] <@ (select array_agg(s.v) from stuff s WHERE s.
   test_id= t.id)
   ;
   
   select * from test t
   WHERE NOT ARRAY['x', 'y']::varchar[] <@ (select array_agg(s.v) from stuff s 
   WHERE s.test_id = t.id)
   ;
   
   select * from test t
   WHERE NOT ARRAY['x', 'y', 'z']::varchar[] <@ (select array_agg(s.v) from stuff 
   s WHERE s.test_id = t.id)
   ;
   
   select * from test t
   WHERE NOT ARRAY ['x', 'y', 'z', 't']::varchar[] <@ (select array_agg(s.v) from 
   stuffs WHERE s.test_id = t.id)
   ;
   
   -- This works, but I'd rather not do the extra EXISTS
   select * from test t
   WHERE (NOT ARRAY ['x', 'y', 'z', 't']::varchar[] <@ (select array_agg(s.v) from
   stuffs WHERE s.test_id = t.id)
   OR NOT EXISTS (
   select * from stuff s where s.test_id = t.id
   )
    )
   ;
   
   
   
   So, I want to return all entries in test not having any of ARRAY ['x', 'y', 
   'z', 't'] referenced in the table stuff, and I'd like to have test.id="d" 
   returned as well, but in order to do that I need to execute the “or not 
   exists”-query. Is it possible to avoid that?
   
   
   
   
   
   
   --
   Andreas Joseph Krogh
   CTO / Partner - Visena AS
   Mobile: +47 909 56 963
   andreas@visena.com <mailto:andreas@visena.com>
   www.visena.com <https://www.visena.com>
    <https://www.visena.com>

2. Re: How to eliminate extra "NOT EXISTS"-query here?

   Tom Lane <tgl@sss.pgh.pa.us> — 2023-11-25T16:08:28Z

   Andreas Joseph Krogh <andreas@visena.com> writes:
   > -- This works, but I'd rather not do the extra EXISTS
   > select * from test t
   > WHERE (NOT ARRAY ['x', 'y', 'z', 't']::varchar[] <@ (select array_agg(s.v) from
   > stuffs WHERE s.test_id = t.id)
   > OR NOT EXISTS (
   > select * from stuff s where s.test_id = t.id
   > )
   >  )
   > ;
   
   > So, I want to return all entries in test not having any of ARRAY ['x', 'y', 
   > 'z', 't'] referenced in the table stuff, and I'd like to have test.id="d" 
   > returned as well, but in order to do that I need to execute the “or not 
   > exists”-query. Is it possible to avoid that?
   
   Probably not directly, but perhaps you could improve the performance of
   this query by converting the sub-selects into a left join:
   
   select * from test t
     left join
       (select s.test_id, array_agg(s.v) as arr from stuffs group by s.test_id) ss
     on ss.test_id = t.id
   WHERE (NOT ARRAY ['x', 'y', 'z', 't']::varchar[] <@ ss.arr)
         OR ss.test_id IS NULL;
   
   Another possibility is
   
   ...
   WHERE (ARRAY ['x', 'y', 'z', 't']::varchar[] <@ ss.arr) IS NOT TRUE
   
   but I don't think that's more readable really, and it will save little.
   
   In either case, this would result in computing array_agg once for
   each group of test_id values in "stuffs", while your original computes
   a similar aggregate for each row in "test".  So whether this is better
   depends on the relative sizes of the tables, although my proposal
   avoids random access to "stuffs" so it will have some advantage.
   
   			regards, tom lane
   
   
   
   

3. Re: How to eliminate extra "NOT EXISTS"-query here?

   hector vass <hector.vass@gmail.com> — 2023-11-25T16:52:51Z

   Not sure you need to use array why not simple table joins, so a table with
   your criteria x y z t joined to stuff to give you candidates that do match,
   then left join with coalesce to add the 'd'
   
   select
   
   --a.id,b.test_id,
   
   coalesce(a.id,b.test_id) as finalresult
   
   from test a
   
   left join (
   
   select
   
   test_id
   
   from stuff a
   
   inner join (values ('x'),('y'),('z'),('t')) b (v) using(v)
   
   group by 1
   
   )b on(a.id=b.test_id);
   
   
   Regards
   Hector Vass
   
   
   
   On Sat, Nov 25, 2023 at 4:08 PM Tom Lane <tgl@sss.pgh.pa.us> wrote:
   
   > Andreas Joseph Krogh <andreas@visena.com> writes:
   > > -- This works, but I'd rather not do the extra EXISTS
   > > select * from test t
   > > WHERE (NOT ARRAY ['x', 'y', 'z', 't']::varchar[] <@ (select
   > array_agg(s.v) from
   > > stuffs WHERE s.test_id = t.id)
   > > OR NOT EXISTS (
   > > select * from stuff s where s.test_id = t.id
   > > )
   > >  )
   > > ;
   >
   > > So, I want to return all entries in test not having any of ARRAY ['x',
   > 'y',
   > > 'z', 't'] referenced in the table stuff, and I'd like to have test.id="d"
   >
   > > returned as well, but in order to do that I need to execute the “or not
   > > exists”-query. Is it possible to avoid that?
   >
   > Probably not directly, but perhaps you could improve the performance of
   > this query by converting the sub-selects into a left join:
   >
   > select * from test t
   >   left join
   >     (select s.test_id, array_agg(s.v) as arr from stuffs group by
   > s.test_id) ss
   >   on ss.test_id = t.id
   > WHERE (NOT ARRAY ['x', 'y', 'z', 't']::varchar[] <@ ss.arr)
   >       OR ss.test_id IS NULL;
   >
   > Another possibility is
   >
   > ...
   > WHERE (ARRAY ['x', 'y', 'z', 't']::varchar[] <@ ss.arr) IS NOT TRUE
   >
   > but I don't think that's more readable really, and it will save little.
   >
   > In either case, this would result in computing array_agg once for
   > each group of test_id values in "stuffs", while your original computes
   > a similar aggregate for each row in "test".  So whether this is better
   > depends on the relative sizes of the tables, although my proposal
   > avoids random access to "stuffs" so it will have some advantage.
   >
   >                         regards, tom lane
   >
   >
   >
   

4. Re: How to eliminate extra "NOT EXISTS"-query here?

   Andreas Joseph Krogh <andreas@visena.com> — 2023-11-25T17:18:57Z

   
   På lørdag 25. november 2023 kl. 17:08:28, skrev Tom Lane <tgl@sss.pgh.pa.us 
   <mailto:tgl@sss.pgh.pa.us>>:
   Andreas Joseph Krogh <andreas@visena.com> writes:
   > -- This works, but I'd rather not do the extra EXISTS
   > select * from test t
   > WHERE (NOT ARRAY ['x', 'y', 'z', 't']::varchar[] <@ (select array_agg(s.v) 
   from
   > stuffs WHERE s.test_id = t.id)
   > OR NOT EXISTS (
   > select * from stuff s where s.test_id = t.id
   > )
   > )
   > ;
   
   > So, I want to return all entries in test not having any of ARRAY ['x', 'y', 
   > 'z', 't'] referenced in the table stuff, and I'd like to have test.id="d" 
   > returned as well, but in order to do that I need to execute the “or not 
   > exists”-query. Is it possible to avoid that?
   
   Probably not directly, but perhaps you could improve the performance of
   this query by converting the sub-selects into a left join:
   
   select * from test t
    left join
    (select s.test_id, array_agg(s.v) as arr from stuffs group by s.test_id) ss
    on ss.test_id = t.id
   WHERE (NOT ARRAY ['x', 'y', 'z', 't']::varchar[] <@ ss.arr)
    OR ss.test_id IS NULL;
   
   Another possibility is
   
   ...
   WHERE (ARRAY ['x', 'y', 'z', 't']::varchar[] <@ ss.arr) IS NOT TRUE
   
   but I don't think that's more readable really, and it will save little.
   
   In either case, this would result in computing array_agg once for
   each group of test_id values in "stuffs", while your original computes
   a similar aggregate for each row in "test". So whether this is better
   depends on the relative sizes of the tables, although my proposal
   avoids random access to "stuffs" so it will have some advantage.
   
   regards, tom lane
   Excellent, thanks!
   
   
   
   
   
   
   --
   Andreas Joseph Krogh
   CTO / Partner - Visena AS
   Mobile: +47 909 56 963
   andreas@visena.com <mailto:andreas@visena.com>
   www.visena.com <https://www.visena.com>
    <https://www.visena.com>
   

5. Re: How to eliminate extra "NOT EXISTS"-query here?

   Dominique Devienne <ddevienne@gmail.com> — 2023-11-27T09:29:46Z

   On Sat, Nov 25, 2023 at 5:53 PM hector vass <hector.vass@gmail.com> wrote:
   
   > Not sure you need to use array why not simple table joins, so a table with
   > your criteria x y z t joined to stuff to give you candidates that do match,
   > then left join with coalesce to add the 'd'
   >
   > select
   >
   > --a.id,b.test_id,
   >
   > coalesce(a.id,b.test_id) as finalresult
   >
   > from test a
   >
   > left join (
   >
   > select
   >
   > test_id
   >
   > from stuff a
   >
   > inner join (values ('x'),('y'),('z'),('t')) b (v) using(v)
   >
   > group by 1
   >
   > )b on(a.id=b.test_id);
   >
   
   Hi Hector. Hopefully this is not a stupid question...
   
   How is that equivalent from the `NOT ARRAY ... <@ ...` though?
   The inner-join-distinct above will return test_id's on any match, but you
   can't know if all array values are matches. Which is different from
   
   > Is the first array contained by the second
   
   from the <@ operator, no?
   I'm unfamiliar with these operators, so am I missing something?
   Just trying to understand the logic here. Thanks, --DD
   

6. Re: How to eliminate extra "NOT EXISTS"-query here?

   hector vass <hector.vass@gmail.com> — 2023-11-28T14:14:05Z

   Not equivalent to the use of NOT ARRAY and entirely possible I have
   misunderstood the requirement ...do you have some more test cases the non
   array solution does not work for
   
   Regards
   Hector Vass
   07773 352559
   
   
   On Mon, Nov 27, 2023 at 9:29 AM Dominique Devienne <ddevienne@gmail.com>
   wrote:
   
   > On Sat, Nov 25, 2023 at 5:53 PM hector vass <hector.vass@gmail.com> wrote:
   >
   >> Not sure you need to use array why not simple table joins, so a table
   >> with your criteria x y z t joined to stuff to give you candidates that do
   >> match, then left join with coalesce to add the 'd'
   >>
   >> select
   >>
   >> --a.id,b.test_id,
   >>
   >> coalesce(a.id,b.test_id) as finalresult
   >>
   >> from test a
   >>
   >> left join (
   >>
   >> select
   >>
   >> test_id
   >>
   >> from stuff a
   >>
   >> inner join (values ('x'),('y'),('z'),('t')) b (v) using(v)
   >>
   >> group by 1
   >>
   >> )b on(a.id=b.test_id);
   >>
   >
   > Hi Hector. Hopefully this is not a stupid question...
   >
   > How is that equivalent from the `NOT ARRAY ... <@ ...` though?
   > The inner-join-distinct above will return test_id's on any match, but you
   > can't know if all array values are matches. Which is different from
   >
   > > Is the first array contained by the second
   >
   > from the <@ operator, no?
   > I'm unfamiliar with these operators, so am I missing something?
   > Just trying to understand the logic here. Thanks, --DD
   >