[Semediawiki-user] Property Chain fails to return existing values

[Michael E. <er...@di...>]

Hello list,

My wiki cannot find values for a property chain (although the values do 
exist).

Q1 This query returns many empty values for "CityName" (the City column, 
though has values)

    {{#ask:  [[Kategorie:House]]
      |?City.CityName=CityName
      |?City
      |format=broadtable
    }}

Q2 Whereas this query always returns values for "CityName"

    {{#ask:  [[Kategorie:House]] [[City::City_43]]
      |?City.CityName=CityName
      |?City
      |format=broadtable
    }}

More specifically: The second query returns values for "CityName" even 
for cases in which the first one is not showing anything. And Q2 is 
correct. Updating either the House or the City page does not change this 
behavior. Other SMW queries with property chains seem to work fine.

I am at my wits' end. This looks like an SMW bug to me. But I cannot 
believe it has not been spotted before.

I run SMW 3.2.3 on MW 1.35.4 with PHP 7.3.33 and MariaDB 10.4.22.

In case it helps, here is the output of DEBUG for both queries

Q1

    Debug output SQLStore
    ASK Query
    [[Kategorie:House]]
    SQL Query
    SELECT DISTINCT
       t0.smw_id AS id,
       t0.smw_title AS t,
       t0.smw_namespace AS ns,
       t0.smw_iw AS iw,
       t0.smw_subobject AS so,
       t0.smw_sortkey AS sortkey, t0.smw_sort
    FROM
       `smw_object_ids` AS t0
    INNER JOIN
    	(`smw_fpt_inst` AS t1
    		INNER JOIN `t2` AS t2 ON t1.o_id=t2.id		
    	) ON t0.smw_id=t1.s_id
    WHERE
       t0.smw_iw!=':smw'
       AND t0.smw_iw!=':smw-delete'
       AND t0.smw_iw!=':smw-redi'
    ORDER BY
       t0.smw_sort ASC
    LIMIT
       205
    OFFSET
       0
    SQL Explain
    ID	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
    1	SIMPLE	t2	ALL	PRIMARY				4		Using temporary; Using filesort
    1	SIMPLE	t1	ref	s_id, o_id, s_id_2, o_id_2	o_id_2	5	wikidb2021.t2.id	3079		Using index
    1	SIMPLE	t0	eq_ref	PRIMARY, smw_id, smw_iw, smw_iw_2	PRIMARY	4	wikidb2021.t1.s_id	1		Using where
    Auxilliary Tables
         Temporary table t2
           Recursively computed hierarchy for element(s) (512).
           SELECT s_id FROM `smw_fpt_subc` WHERE o_id=512 LIMIT 1
    Query Metrics
    Query-Size:1
    Query-Depth:0
    Errors and Warnings
    None

Q2

    Debug output SQLStore
    ASK Query
    [[Kategorie:House]] [[City::City 43]]
    SQL Query
    SELECT DISTINCT
       t0.smw_id AS id,
       t0.smw_title AS t,
       t0.smw_namespace AS ns,
       t0.smw_iw AS iw,
       t0.smw_subobject AS so,
       t0.smw_sortkey AS sortkey, t0.smw_sort
    FROM
       `smw_object_ids` AS t0
    INNER JOIN
    	(`smw_fpt_inst` AS t1
    		INNER JOIN `t2` AS t2 ON t1.o_id=t2.id
    		INNER JOIN `smw_di_wikipage` AS t4 ON t1.s_id=t4.s_id
    	) ON t0.smw_id=t1.s_id
    WHERE
       (
        (t4.p_id=845 AND t4.o_id=19928)
       )
       AND t0.smw_iw!=':smw'
       AND t0.smw_iw!=':smw-delete'
       AND t0.smw_iw!=':smw-redi'
    ORDER BY
       t0.smw_sort ASC
    LIMIT
       205
    OFFSET
       0
    SQL Explain
    ID	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
    1	SIMPLE	t4	ref	s_id, o_id, p_id, s_id_2, s_id_3, o_id_2, o_id_3	o_id	5	const	231		Using where; Using temporary; Using filesort
    1	SIMPLE	t0	eq_ref	PRIMARY, smw_id, smw_iw, smw_iw_2	PRIMARY	4	wikidb2021.t4.s_id	1		Using where
    1	SIMPLE	t1	ref	s_id, o_id, s_id_2, o_id_2	s_id_2	4	wikidb2021.t4.s_id	1		Using index
    1	SIMPLE	t2	ALL	PRIMARY				4		Using where; Using join buffer (flat, BNL join)
    Auxilliary Tables
         Temporary table t2
           Recursively computed hierarchy for element(s) (512).
           SELECT s_id FROM `smw_fpt_subc` WHERE o_id=512 LIMIT 1
    Query Metrics
    Query-Size:3
    Query-Depth:1
    Errors and Warnings
    None

Any feedback greatly appreciated.

CU,
     michael

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