HHH-9301 - Support select variable refs in group by for DBMS dialects that support it

While not strictly compliant with the SQL specification, the MySQL, PostgreSQL and H2 support the use of select aliases in the GROUP BY clause. An obvious benefit is that produced SQL queries will be easier to read, because complex select expressions from aggregrate queries will have to be included in the group by clause as well. These can now simply reference the aliases of the respective columns for the tuple element. However, there is also a functional difference. For function invocations that have parameterized arguments, the query optimizer can't guarantee the that the function result between the selection projection and grouping process are equal. This results in an error because a value is projected which is not grouped by. An example where this for example becomes relevant, is when parameterizing TimeScaleDB's [`time_bucket_gapfill()`](https://docs.timescale.com/latest/api#time_bucket_gapfill-examples) function.

For example, using `time_bucket_gapfill()` one might want to produce a criteria query that produces the following SQL:

```sql
SELECT
    time_bucket_gapfill(?, time, ?, ?) AS ts,
    avg(tg) as tg
FROM iaqmeasurement
GROUP BY ts
ORDER BY ts;
```

When the alias is not used as grouping value, the query will yield an error:

```sql
SELECT
    time_bucket_gapfill(?, time, ?, ?) AS ts,
    avg(tg) as tg
FROM iaqmeasurement
GROUP BY time_bucket_gapfill(?, time, ?, ?)
ORDER BY ts;
```

Of course the parameter values can just be stored in a CTE as well, but I think we should consider support for variable refs in group by for DBMS dialects that support it. This pull request implements the feature equivalently to how its currently done for order by clauses, and only enables the feature for known supported dialects (H2, PostgreSQL and MySQL - based on [https://stackoverflow.com/a/3841804/2104280](https://stackoverflow.com/a/3841804/2104280)).

Jira: https://hibernate.atlassian.net/browse/HHH-9301

Co-authored-by: Sayra Ranjha <S.S.Ranjha@student.tudelft.nl>

hibernate-core/src/main/antlr/hql-sql.g

@@ -237,6 +237,10 @@ tokens
 		return false;
 	}
 
+	protected boolean isGroupExpressionResultVariableRef(AST ident) throws SemanticException {
+		return false;
+	}
+
 	protected void handleResultVariableRef(AST resultVariableRef) throws SemanticException {
 	}
 
@@ -394,7 +398,7 @@ resultVariableRef!
 	;
 
 groupClause
-	: #(GROUP { handleClauseStart( GROUP ); } (expr [ null ])+ ( #(HAVING logicalExpr) )? ) {
+	: #(GROUP { handleClauseStart( GROUP ); } ({ isGroupExpressionResultVariableRef( _t ) }? resultVariableRef | expr [ null ])+ ( #(HAVING logicalExpr) )? ) {
 		handleClauseEnd();
 	}
 	;

hibernate-core/src/main/java/org/hibernate/dialect/Dialect.java

@@ -3048,4 +3048,9 @@ public abstract class Dialect implements ConversionContext {
 	protected String prependComment(String sql, String comment) {
 		return  "/* " + comment + " */ " + sql;
 	}
+
+	public boolean supportsSelectAliasInGroupByClause() {
+		return false;
+	}
+
 }

hibernate-core/src/main/java/org/hibernate/dialect/H2Dialect.java

@@ -450,4 +450,10 @@ public class H2Dialect extends Dialect {
 	public String getQueryHintString(String query, String hints) {
 		return IndexQueryHintHandler.INSTANCE.addQueryHints( query, hints );
 	}
+
+	@Override
+	public boolean supportsSelectAliasInGroupByClause() {
+		return true;
+	}
+
 }

hibernate-core/src/main/java/org/hibernate/dialect/MySQLDialect.java

@@ -604,4 +604,10 @@ public class MySQLDialect extends Dialect {
 	protected String escapeLiteral(String literal) {
 		return ESCAPE_PATTERN.matcher( super.escapeLiteral( literal ) ).replaceAll( ESCAPE_PATTERN_REPLACEMENT );
 	}
+
+	@Override
+	public boolean supportsSelectAliasInGroupByClause() {
+		return true;
+	}
+
 }

hibernate-core/src/main/java/org/hibernate/dialect/PostgreSQL81Dialect.java

@@ -643,4 +643,10 @@ public class PostgreSQL81Dialect extends Dialect {
 	public boolean supportsJdbcConnectionLobCreation(DatabaseMetaData databaseMetaData) {
 		return false;
 	}
+
+	@Override
+	public boolean supportsSelectAliasInGroupByClause() {
+		return true;
+	}
+
 }

hibernate-core/src/main/java/org/hibernate/hql/internal/ast/HqlSqlWalker.java

@@ -1267,6 +1267,18 @@ public class HqlSqlWalker extends HqlSqlBaseWalker implements ErrorReporter, Par
 		return false;
 	}
 
+	@Override
+	protected boolean isGroupExpressionResultVariableRef(AST groupExpressionNode) throws SemanticException {
+		// Aliases are not sensible in subqueries
+		if ( getDialect().supportsSelectAliasInGroupByClause() &&
+				!isSubQuery() &&
+				groupExpressionNode.getType() == IDENT &&
+				selectExpressionsByResultVariable.containsKey( groupExpressionNode.getText() ) ) {
+			return true;
+		}
+		return false;
+	}
+
 	@Override
 	protected void handleResultVariableRef(AST resultVariableRef) throws SemanticException {
 		if ( isSubQuery() ) {

hibernate-core/src/test/java/org/hibernate/query/GroupByAliasTest.java

@@ -0,0 +1,228 @@
+/*
+ * Hibernate, Relational Persistence for Idiomatic Java
+ *
+ * License: GNU Lesser General Public License (LGPL), version 2.1 or later.
+ * See the lgpl.txt file in the root directory or <http://www.gnu.org/licenses/lgpl-2.1.html>.
+ */
+package org.hibernate.query;
+
+import org.hibernate.jpa.test.BaseEntityManagerFunctionalTestCase;
+import org.hibernate.testing.DialectChecks;
+import org.hibernate.testing.RequiresDialectFeature;
+import org.hibernate.testing.jdbc.SQLStatementInterceptor;
+import org.junit.Test;
+
+import javax.persistence.CascadeType;
+import javax.persistence.Entity;
+import javax.persistence.Id;
+import javax.persistence.IdClass;
+import javax.persistence.ManyToOne;
+import javax.persistence.Tuple;
+import java.io.Serializable;
+import java.util.List;
+import java.util.Map;
+import java.util.Objects;
+
+import static org.hibernate.testing.transaction.TransactionUtil.doInJPA;
+import static org.junit.Assert.assertNotNull;
+
+/**
+ * @author Jan-Willem Gmelig Meyling
+ * @author Sayra Ranjha
+ */
+@RequiresDialectFeature(value = DialectChecks.SupportsSelectAliasInGroupByClause.class, jiraKey = "HHH-9301")
+public class GroupByAliasTest extends BaseEntityManagerFunctionalTestCase {
+
+	public static final int MAX_COUNT = 15;
+
+	private SQLStatementInterceptor sqlStatementInterceptor;
+
+	@Override
+	protected void addConfigOptions(Map options) {
+		sqlStatementInterceptor = new SQLStatementInterceptor( options );
+	}
+
+	@Override
+	public Class[] getAnnotatedClasses() {
+		return new Class[] {
+			Person.class,
+			Association.class
+		};
+	}
+
+	@Override
+	protected void afterEntityManagerFactoryBuilt() {
+		doInJPA( this::entityManagerFactory, entityManager -> {
+			for ( int i = 0; i < MAX_COUNT; i++ ) {
+				Association association = new Association();
+				association.setId( i );
+				association.setName(String.format( "Association nr %d", i ) );
+
+				Person person = new Person();
+				person.setId( i );
+				person.setName( String.format( "Person nr %d", i ) );
+				person.setAssociation(association);
+				person.setAge(5);
+				entityManager.persist( person );
+			}
+		} );
+	}
+
+	@Test
+	public void testSingleIdAlias() {
+		sqlStatementInterceptor.clear();
+
+		List<Tuple> list = doInJPA(this::entityManagerFactory, entityManager -> {
+			return entityManager.createQuery(
+					"select p.id as id_alias, sum(p.age) " +
+							"from Person p group by id_alias order by id_alias", Tuple.class)
+					.getResultList();
+		});
+
+		String s = sqlStatementInterceptor.getSqlQueries().get(0);
+		assertNotNull(s);
+	}
+
+	@Test
+	public void testCompoundIdAlias() {
+		sqlStatementInterceptor.clear();
+
+		List<Tuple> list = doInJPA(this::entityManagerFactory, entityManager -> {
+			return entityManager.createQuery(
+					"select p.association as id_alias, sum(p.age) " +
+							"from Person p group by id_alias order by id_alias", Tuple.class)
+					.getResultList();
+		});
+
+		String s = sqlStatementInterceptor.getSqlQueries().get(0);
+		assertNotNull(s);
+	}
+
+
+	@Test
+	public void testMultiIdAlias() {
+		sqlStatementInterceptor.clear();
+
+		List<Tuple> list = doInJPA(this::entityManagerFactory, entityManager -> {
+			return entityManager.createQuery(
+					"select p.id as id_alias_1, p.association as id_alias_2, sum(p.age) " +
+							"from Person p group by id_alias_1, id_alias_2 order by id_alias_1, id_alias_2 ", Tuple.class)
+					.getResultList();
+		});
+
+		String s = sqlStatementInterceptor.getSqlQueries().get(0);
+		assertNotNull(s);
+	}
+
+	@Entity(name = "Person")
+	public static class Person {
+
+		@Id
+		private Integer id;
+
+		private String name;
+
+		private Integer age;
+
+		@ManyToOne(cascade = CascadeType.PERSIST)
+		private Association association;
+
+		public Integer getId() {
+			return id;
+		}
+
+		public void setId(Integer id) {
+			this.id = id;
+		}
+
+		public String getName() {
+			return name;
+		}
+
+		public void setName(String name) {
+			this.name = name;
+		}
+
+		public Integer getAge() {
+			return age;
+		}
+
+		public void setAge(Integer age) {
+			this.age = age;
+		}
+
+		public Association getAssociation() {
+			return association;
+		}
+
+		public void setAssociation(Association association) {
+			this.association = association;
+		}
+	}
+
+
+	@IdClass(Association.IdClass.class)
+	@Entity(name = "Association")
+	public static class Association {
+
+		public static class IdClass implements Serializable {
+			private Integer id;
+			private String name;
+
+			public Integer getId() {
+				return id;
+			}
+
+			public void setId(Integer id) {
+				this.id = id;
+			}
+
+			public String getName() {
+				return name;
+			}
+
+			public void setName(String name) {
+				this.name = name;
+			}
+
+			@Override
+			public boolean equals(Object o) {
+				if (this == o) return true;
+				if (o == null || getClass() != o.getClass()) return false;
+				IdClass id1 = (IdClass) o;
+				return Objects.equals(id, id1.id) &&
+						Objects.equals(name, id1.name);
+			}
+
+			@Override
+			public int hashCode() {
+				return Objects.hash(id, name);
+			}
+		}
+
+		@Id
+		private Integer id;
+
+		@Id
+		private String name;
+
+
+		public Integer getId() {
+			return id;
+		}
+
+		public void setId(Integer id) {
+			this.id = id;
+		}
+
+		public String getName() {
+			return name;
+		}
+
+		public void setName(String name) {
+			this.name = name;
+		}
+
+	}
+
+}

hibernate-testing/src/main/java/org/hibernate/testing/DialectChecks.java

@@ -266,6 +266,12 @@ abstract public class DialectChecks {
 		}
 	}
 
+	public static class SupportsSelectAliasInGroupByClause implements DialectCheck {
+		public boolean isMatch(Dialect dialect) {
+			return dialect.supportsSelectAliasInGroupByClause();
+		}
+	}
+
 	public static class SupportsNClob implements DialectCheck {
 		@Override
 		public boolean isMatch(Dialect dialect) {