diff --git a/backend/src/main/java/com/bakdata/conquery/sql/conversion/model/aggregator/CommonAggregationSelect.java b/backend/src/main/java/com/bakdata/conquery/sql/conversion/model/aggregator/CommonAggregationSelect.java
index 01e53a2f08..3197d95532 100644
--- a/backend/src/main/java/com/bakdata/conquery/sql/conversion/model/aggregator/CommonAggregationSelect.java
+++ b/backend/src/main/java/com/bakdata/conquery/sql/conversion/model/aggregator/CommonAggregationSelect.java
@@ -8,6 +8,7 @@
 import com.bakdata.conquery.sql.conversion.model.QueryStep;
 import com.bakdata.conquery.sql.conversion.model.select.ConnectorSqlSelects;
 import com.bakdata.conquery.sql.conversion.model.select.FieldWrapper;
+import com.bakdata.conquery.sql.conversion.model.select.SingleColumnSqlSelect;
 import com.bakdata.conquery.sql.conversion.model.select.SqlSelect;
 import lombok.Getter;
 
@@ -23,23 +24,23 @@
 @Getter
 class CommonAggregationSelect<T> {
 
-	private final List<? extends SqlSelect> rootSelects;
+	private final List<SingleColumnSqlSelect> rootSelects;
 	private final FieldWrapper<T> groupBy;
 	private final QueryStep additionalPredecessor;
 
-	public CommonAggregationSelect(List<? extends SqlSelect> rootSelects, FieldWrapper<T> groupBy, QueryStep additionalPredecessor) {
+	public CommonAggregationSelect(List<SingleColumnSqlSelect> rootSelects, FieldWrapper<T> groupBy, QueryStep additionalPredecessor) {
 		this.rootSelects = rootSelects;
 		this.groupBy = groupBy;
 		this.additionalPredecessor = additionalPredecessor;
 	}
 
-	public CommonAggregationSelect(SqlSelect rootSelect, FieldWrapper<T> groupBy) {
+	public CommonAggregationSelect(SingleColumnSqlSelect rootSelect, FieldWrapper<T> groupBy) {
 		this.rootSelects = List.of(rootSelect);
 		this.groupBy = groupBy;
 		this.additionalPredecessor = null;
 	}
 
-	public CommonAggregationSelect(List<? extends SqlSelect> rootSelects, FieldWrapper<T> groupBy) {
+	public CommonAggregationSelect(List<SingleColumnSqlSelect> rootSelects, FieldWrapper<T> groupBy) {
 		this.rootSelects = rootSelects;
 		this.groupBy = groupBy;
 		this.additionalPredecessor = null;
diff --git a/backend/src/main/java/com/bakdata/conquery/sql/conversion/model/aggregator/SumSqlAggregator.java b/backend/src/main/java/com/bakdata/conquery/sql/conversion/model/aggregator/SumSqlAggregator.java
index 93accb556a..2659095928 100644
--- a/backend/src/main/java/com/bakdata/conquery/sql/conversion/model/aggregator/SumSqlAggregator.java
+++ b/backend/src/main/java/com/bakdata/conquery/sql/conversion/model/aggregator/SumSqlAggregator.java
@@ -30,6 +30,7 @@
 import com.bakdata.conquery.sql.conversion.model.select.FieldWrapper;
 import com.bakdata.conquery.sql.conversion.model.select.SelectContext;
 import com.bakdata.conquery.sql.conversion.model.select.SelectConverter;
+import com.bakdata.conquery.sql.conversion.model.select.SingleColumnSqlSelect;
 import lombok.Getter;
 import lombok.RequiredArgsConstructor;
 import org.jooq.Condition;
@@ -187,7 +188,7 @@ public Condition convertForTableExport(SumFilter<RANGE> filter, FilterContext<RA
 	private CommonAggregationSelect<BigDecimal> createSumAggregationSelect(Column sumColumn, Column subtractColumn, String alias, ConnectorSqlTables tables) {
 
 		Class<? extends Number> numberClass = NumberMapUtil.NUMBER_MAP.get(sumColumn.getType());
-		List<ExtractingSqlSelect<?>> preprocessingSelects = new ArrayList<>();
+		List<SingleColumnSqlSelect> preprocessingSelects = new ArrayList<>();
 
 		ExtractingSqlSelect<? extends Number> rootSelect = new ExtractingSqlSelect<>(tables.getRootTable(), sumColumn.getName(), numberClass);
 		preprocessingSelects.add(rootSelect);
@@ -223,13 +224,13 @@ private CommonAggregationSelect<BigDecimal> createDistinctSumAggregationSelect(
 			ConnectorSqlTables tables,
 			NameGenerator nameGenerator
 	) {
-		List<ExtractingSqlSelect<?>> preprocessingSelects = new ArrayList<>();
+		List<SingleColumnSqlSelect> preprocessingSelects = new ArrayList<>();
 
 		Class<? extends Number> numberClass = NumberMapUtil.NUMBER_MAP.get(sumColumn.getType());
 		ExtractingSqlSelect<? extends Number> rootSelect = new ExtractingSqlSelect<>(tables.getRootTable(), sumColumn.getName(), numberClass);
 		preprocessingSelects.add(rootSelect);
 
-		List<ExtractingSqlSelect<?>> distinctByRootSelects =
+		List<SingleColumnSqlSelect> distinctByRootSelects =
 				distinctByColumns.stream()
 								 .map(column -> new ExtractingSqlSelect<>(tables.getRootTable(), column.getName(), Object.class))
 								 .collect(Collectors.toList());
@@ -249,15 +250,15 @@ private CommonAggregationSelect<BigDecimal> createDistinctSumAggregationSelect(
 	 */
 	private static QueryStep createRowNumberCte(
 			SqlIdColumns ids,
-			ExtractingSqlSelect<? extends Number> sumColumnRootSelect,
-			List<ExtractingSqlSelect<?>> distinctByRootSelects,
+			SingleColumnSqlSelect sumColumnRootSelect,
+			List<SingleColumnSqlSelect> distinctByRootSelects,
 			String alias,
 			SqlTables connectorTables,
 			NameGenerator nameGenerator
 	) {
 		String predecessor = connectorTables.getPredecessor(ConceptCteStep.AGGREGATION_SELECT);
 		SqlIdColumns qualifiedIds = ids.qualify(predecessor);
-		ExtractingSqlSelect<?> qualifiedSumRootSelect = sumColumnRootSelect.qualify(predecessor);
+		SingleColumnSqlSelect qualifiedSumRootSelect = sumColumnRootSelect.qualify(predecessor);
 
 		List<Field<?>> partitioningFields = Stream.concat(
 														  qualifiedIds.toFields().stream(),