Re: DISTINCT in STRING_AGG

["John J. Turner" <fenwayriffs@xxxxxxxxx>]

On Nov 28, 2015, at 1:35 PM, Sterpu Victor <victor@xxxxxxxx> wrote:

Hello

 

Can I make a distinct STRING_AGG?

This is my query :

SELECT atjs.id, STRING_AGG(CAST(aqjs1.id AS VARCHAR), ',' ORDER BY aqjs1.to_left) AS children

FROM administration.ad_query_join_select atjs 
JOIN administration.ad_query aq ON (aq.id=atjs.id_ad_query) 
LEFT JOIN administration.ad_query_join_select aqjs1 ON (aqjs1.id_ad_query = atjs.id_ad_query AND aqjs1.to_left>atjs.to_left AND aqjs1.to_right<atjs.to_right) 
LEFT JOIN administration.ad_query_join_select aqjs2 ON (aqjs2.id_ad_query = atjs.id_ad_query AND aqjs2.to_left>atjs.to_left AND aqjs2.to_right<atjs.to_right AND aqjs2.to_left<aqjs1.to_left AND aqjs2.to_right>aqjs1.to_right) 
LEFT JOIN administration.ad_query_join_select aqjs3 ON (aqjs3.id_ad_query = atjs.id_ad_query AND aqjs3.to_left<atjs.to_left AND aqjs3.to_right>atjs.to_right)

WHERE aqjs2.id IS NULL AND atjs.id_ad_query = 475543
GROUP BY aq.id, atjs.id 
ORDER BY aq.id ASC, atjs.to_left ASC;

 

And "childen" contain doubles. The result is:

id          ; children

1399029;"1399031,1399031"
1399031;"1399032,1399032,1399032,1399033,1399033,1399033"

 

There are doubles because of the join aqjs3 witch is producing this problem.Can I make it so the children ID's are unique?

Just to mention, this looks like a good candidate for range types and CTE’s.

The > / < comparisons appear to be mutually exclusive in each LEFT JOIN clause, so it’s not apparent why aqjs3 is causing duplication, as you’ve stated.

As far as I can see, without providing us with your table constraints/keys, there’s no way to determine what makes your ID values unique…

However, if you defer your STRING_AGG until after you derive a distinct “staging” result set from the joins, then you can effect uniqueness -

e.g. (air code):

   WITH q AS 

      (SELECT aq.id aq_parent_id, atjs.id atjs_parent_id, CAST(aqjs1.id AS VARCHAR) child FROM ... GROUP BY aq.id, atjs.id, aqjs1.id)

   SELECT atjs_parent_id, STRING_AGG(child,’,’ ORDER BY aqjs.to_left) children 

   FROM q LEFT JOIN (SELECT DISTINCT id_ad_query, to_left FROM administration.ad_query_join_select) aqjs ON …

   GROUP BY aq_parent_id, parent

   ORDER BY aq_parent_id, atjs.to_left;

Something along these lines ‘may’ produce a unique set of child values for each id by which to perform a STRING_AGG on, but again, I can only guess based on the lack of definition provided for your table constraints.

John