Something like this:

SELECT Array_Agg( a )
FROM (  SELECT  ARRAY   [ 1, 2, 3] a
        UNION
        SELECT  ARRAY   [ 2, 3, 4] a  )
;

Unfortunately, H2 does not seem to support any Flatten or Concat-
Aggregate function for arrays.
And UNNEST() is not deep.

So I am indeed not sure if this can be currently done with H2, sorry.

On Sat, 2024-07-20 at 18:04 +0700, Andreas Reichel wrote:
> Greetings!
> 
> Would you not need to Aggregate the Array Columns first e.g. using
> `ARRAY_AGG` (or a similar function) to get 1 huge array and then to
> unnest it?
> Also, there should be an array function making the array itself
> distinct already.
> 
> Best regards
> Andreas
> 
> 
> On Sat, 2024-07-20 at 10:46 +0000, 'Peter Borissow' via H2 Database
> wrote:
> > Hello,
> >     I have a simple query in PostgreSQL that I am trying to emulate
> > in H2:
> > SELECT DISTINCT(unnest(tags)) as tags FROM company;
> > 
> > The "tags" column is a varchar array. The query returns a unique
> > list of tags from the "tags" column.
> > 
> > When I try to run the same query in H2 2.2.224, I get a Function
> > "unnest" not found error
> > 
> > I can get a unique list of tags from a single record like this:
> > SELECT distinct(tags) FROM UNNEST(select tags from company where
> > id=1) as t(tags);
> > 
> > But I'm struggling to come up with a query to get a unique list of
> > tags from multiple records. Any suggestions?
> > 
> > Thanks in advance,
> > Peter
> > 

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