Thanks.  Does this make sense?

   - There are 3 nodes under the Merge Join
   - The first node is an InitPlan, due to the ANY(ARRAY()) - that gets
   executed and finds 0 matching rows
   - The second node is the outer node in the Merge Join and that is the
   expensive node in our query plan
   - The third node is the inner node in the Merge Join and that node
   references the SubPlan generated by the first node. The IndexCond has*
   "id = ANY($2) AND ..."* and the comparison with the result of the
   SubPlan does not find a match, so that's where the short-circuiting happens.

Here are the relevant lines from the node (12) accessing the result of the
SubPlan:

                            "Plans": [
                              {
                                "Node Type": "Index Only Scan",
                                "Parent Relationship": "Outer",
                                "Parallel Aware": false,
                                "Scan Direction": "Forward",
                                "Index Name":
"policyperi_u_id_1mw8mh83lyyd9",
                                "Relation Name": "pc_policyperiod",
                                "Alias": "qroots0",
                                "Startup Cost": 0.69,
                                "Total Cost": 18.15,
                                "Plan Rows": 10,
                                "Plan Width": 8,
                                "Actual Startup Time": 0.045,
                                "Actual Total Time": 0.045,
                                "Actual Rows": 0,
                                "Actual Loops": 1,
                                "Index Cond": "(*(id = ANY ($2)) AND*
(retired = 0) AND (temporarybranch = false))",


Here's the screenshot again:

[image: image.png]

Thanks,
Jerry

On Wed, Dec 20, 2023 at 10:32 AM Frédéric Yhuel <frederic.yh...@dalibo.com>
wrote:

>
>
> Le 20/12/2023 à 15:40, Jerry Brenner a écrit :
> > Whichever side gets executed first, is the execution of the side that
> > would be second get short circuited if 0 rows are returned by the first
> > side?
>
> Indeed, if 0 rows are returned from the outer relation, the scan of the
> inner relation is never executed.
>
> Best regards,
> Frédéric
>
>

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