fix: data export - replace O(n²) org unit descendants cross-join with path index scan [DHIS2-21490] (#23880)

* fix: SQL to add children for all direct matches

* fix: unit test assert

Author: jbee

dhis-2/dhis-services/dhis-service-core/src/main/java/org/hisp/dhis/datavalue/hibernate/HibernateDataExportStore.java

@@ -174,10 +174,9 @@ ou_ids AS (
       ),
       ou_with_descendants_ids AS (
         SELECT DISTINCT ou.organisationunitid
-        FROM organisationunit ou
-        LEFT JOIN organisationunit parent_ou ON (ou.path LIKE parent_ou.path || '%')
-        WHERE ou.organisationunitid IN (SELECT organisationunitid FROM ou_ids)
-             OR parent_ou.organisationunitid IN (SELECT organisationunitid FROM ou_ids)
+        FROM ou_ids
+        JOIN organisationunit root USING (organisationunitid)
+        JOIN organisationunit ou ON ou.path LIKE root.path || '%'
       )
       SELECT
         de.uid AS deid,

dhis-2/dhis-services/dhis-service-core/src/test/java/org/hisp/dhis/datavalue/hibernate/DataExportQueryBuilderTest.java

@@ -298,10 +298,9 @@ ou_ids AS (
         ),
         ou_with_descendants_ids AS (
           SELECT DISTINCT ou.organisationunitid
-          FROM organisationunit ou
-          LEFT JOIN organisationunit parent_ou ON (ou.path LIKE parent_ou.path || '%')
-          WHERE ou.organisationunitid IN (SELECT organisationunitid FROM ou_ids)
-               OR parent_ou.organisationunitid IN (SELECT organisationunitid FROM ou_ids)
+          FROM ou_ids
+          JOIN organisationunit root USING (organisationunitid)
+          JOIN organisationunit ou ON ou.path LIKE root.path || '%'
         )
         SELECT
           de.uid AS deid,
@@ -391,10 +390,9 @@ ou_ids AS (
         ),
         ou_with_descendants_ids AS (
           SELECT DISTINCT ou.organisationunitid
-          FROM organisationunit ou
-          LEFT JOIN organisationunit parent_ou ON (ou.path LIKE parent_ou.path || '%')
-          WHERE ou.organisationunitid IN (SELECT organisationunitid FROM ou_ids)
-               OR parent_ou.organisationunitid IN (SELECT organisationunitid FROM ou_ids)
+          FROM ou_ids
+          JOIN organisationunit root USING (organisationunitid)
+          JOIN organisationunit ou ON ou.path LIKE root.path || '%'
         )
         SELECT
           de.uid AS deid,