hibernate/hibernate-orm · error · UnsupportedOperationException

Summarization is not supported by DBMS

Error message

Summarization is not supported by DBMS

What it means

HQL grouping-set constructs - 'group by rollup(...)', 'cube(...)', 'grouping sets(...)' - become a Summarization AST node. H2LegacySqlAstTranslator.renderPartitionItem must render such expressions when emulating aggregate/window machinery, and for Summarization it throws UnsupportedOperationException: the legacy H2 translator contains no grouping-sets emulation (the source comment notes only an impractical union-all rewrite exists).

Source

Thrown at hibernate-community-dialects/src/main/java/org/hibernate/community/dialect/H2LegacySqlAstTranslator.java:300

		if ( renderAsArray ) {
			append( OPEN_PARENTHESIS );
		}
		super.visitSqlSelections( selectClause );
		if ( renderAsArray ) {
			append( CLOSE_PARENTHESIS );
		}
	}

	@Override
	protected void renderPartitionItem(Expression expression) {
		if ( expression instanceof Literal ) {
			appendSql( "'0' || '0'" );
		}
		else if ( expression instanceof Summarization ) {
			// This could theoretically be emulated by rendering all grouping variations of the query and
			// connect them via union all but that's probably pretty inefficient and would have to happen
			// on the query spec level
			throw new UnsupportedOperationException( "Summarization is not supported by DBMS" );
		}
		else {
			expression.accept( this );
		}
	}

	@Override
	public void visitBinaryArithmeticExpression(BinaryArithmeticExpression arithmeticExpression) {
		appendSql( OPEN_PARENTHESIS );
		visitArithmeticOperand( arithmeticExpression.getLeftHandOperand() );
		appendSql( arithmeticExpression.getOperator().getOperatorSqlTextString() );
		visitArithmeticOperand( arithmeticExpression.getRightHandOperand() );
		appendSql( CLOSE_PARENTHESIS );
	}

	@Override
	protected void visitArithmeticOperand(Expression expression) {
		render( expression, SqlAstNodeRenderingMode.NO_PLAIN_PARAMETER );

View on GitHub (pinned to fad1729dce)

Solutions

  1. Expand the rollup/cube into an explicit UNION ALL of plain group-by queries (one per grouping variation)
  2. Switch the H2 database to the non-legacy dialect (H2 2.x), which supports grouping-set rendering
  3. Precompute subtotals (summary table or in-Java aggregation over detail rows)
  4. Branch the report query per database and use plain group-by on the H2 legacy profile

Example fix

// before (HQL, throws on H2 legacy dialect)
select d.name, count(e) from Employee e join e.dept d group by rollup(d.name)

// after (explicit union of variations)
select d.name, count(e) from Employee e join e.dept d group by d.name
union all
select null, count(e) from Employee e
Defensive patterns

Strategy: validation

Validate before calling

Dialect d = sessionFactory.getJdbcServices().getDialect();
if (d instanceof org.hibernate.community.dialect.H2LegacyDialect
        && (hql.contains("rollup(") || hql.contains("cube(") || hql.contains("grouping sets"))) {
    hql = expandToUnionAll(hql);
}

Type guard

static boolean groupingSetsSafe(Dialect d) {
    return !(d instanceof org.hibernate.community.dialect.H2LegacyDialect);
}

Try / catch

try {
    rows = session.createQuery(hql).getResultList(); // rollup/cube/grouping sets
} catch (UnsupportedOperationException e) {
    if (e.getMessage().contains("Summarization")) {
        // re-run as union-all of plain group-by queries
    } else throw e;
}

Prevention

When it happens

Trigger: HQL with rollup/cube/grouping sets executed under the H2 legacy dialect, e.g. 'select d.name, count(e) from Employee e join e.dept d group by rollup(d.name)', particularly when surrounding query elements (window functions, tuple comparisons) force partition-item rendering.

Common situations: Reporting/subtotal queries written on newer databases but executed in H2-based legacy test suites; migrating an app to Hibernate 6/7 where the H2 test database stayed on the legacy dialect; analytics code sharing between production PostgreSQL and H2 staging.

Related errors

AI-assisted analysis of hibernate/hibernate-orm@fad1729dce (2026-08-22). Data as JSON: /api/errors/8cdefda16fa7f4af. Report an issue: GitHub.