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[GH-444] Do not use group_concat optimization when query has order by clause #445

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Merged
ledsoft merged 1 commit into from
May 28, 2026
Merged

[GH-444] Do not use group_concat optimization when query has order by clause #445

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8 changes: 3 additions & 5 deletions ...ava/cz/cvut/kbss/jopa/query/sparql/loader/AttributeEnumeratingSparqlAssemblyModifier.java
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Original file line number Diff line number Diff line change
Expand Up @@ -114,7 +114,7 @@ private void modifyProjection(TokenQueryParameter<?> firstProjected, TokenStream
boolean hasGroupConcat = false;
for (QueryVariableMapping varMapping : queryMod.variables()) {
// PERF: GROUP_CONCAT may prevent combinatorial blowup of the number of rows
if (varMapping.canGroupConcat()) {
if (!queryAttributes.hasOrderBy() && varMapping.canGroupConcat()) {
projection.append(' ').append(varMapping.generateGroupConcat());
hasGroupConcat = true;
} else {
Expand All @@ -126,10 +126,8 @@ private void modifyProjection(TokenQueryParameter<?> firstProjected, TokenStream
tokenRewriter.insertAfter(firstProjected.getSingleToken(), projection.toString());
if (hasGroupConcat) {
tokenRewriter.insertAfter(queryAttributes.lastClosingCurlyBraceToken(), groupBy.toString());
if (!queryAttributes.hasOrderBy()) {
// Add ordering to ensure stable results with rows with the same subject in sequence
tokenRewriter.insertAfter(queryAttributes.lastClosingCurlyBraceToken(), " ORDER BY " + firstProjected.getIdentifierAsQueryString());
}
// Add ordering to ensure stable results with rows with the same subject in sequence
tokenRewriter.insertAfter(queryAttributes.lastClosingCurlyBraceToken(), " ORDER BY " + firstProjected.getIdentifierAsQueryString());
}
}

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14 changes: 14 additions & 0 deletions ...cz/cvut/kbss/jopa/query/sparql/loader/AttributeEnumeratingSparqlAssemblyModifierTest.java
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Expand Up @@ -298,6 +298,20 @@ void modifyGroupConcatenatesPluralStringAttributeValues() {
assertThat(result, containsString("GROUP BY ?x"));
}

@Test
void modifyDoesNotAddGroupConcatWhenQueryHasOrderBy() {
final TokenStreamSparqlQueryHolder holder = parser.parseQuery("SELECT ?x WHERE { ?x a ?type ; ?hasString ?stringAttribute } ORDER BY ?stringAttribute");
final EntityGraph<OWLClassN> fetchGraph = new EntityGraphImpl<>(metamodelMocks.forOwlClassN()
.entityType(), metamodel);
fetchGraph.addAttributeNodes("pluralAnnotation");
final AttributeEnumeratingSparqlAssemblyModifier sut = createSut(metamodelMocks.forOwlClassN()
.entityType(), new EntityDescriptor(), fetchGraph);
holder.setAssemblyModifier(sut);

final String result = holder.assembleQuery();
assertThat(result, not(containsString("GROUP_CONCAT")));
}

/**
* Simplified Hamcrest matcher that checks if a SPARQL query projects a specific variable. The matcher extracts the
* projection part of the query (everything before the WHERE clause) and checks if it contains the specified
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