Add support for GROUP BY statement

force-app/main/default/classes/Q.cls

@@ -10,6 +10,7 @@ public class Q {
 	private Integer numberOfRowsToSkip;
 
 	private Set<String> fieldList = new Set<String>();
+	private Set<String> groupBy = new Set<String>();
 	private List<QOrder> orders = new List<QOrder>();
 	private List<QCondition> conditions = new List<QCondition>();
 	private List<Q> subQueries = new List<Q>();
@@ -77,6 +78,22 @@ public class Q {
 		return this;
 	}
 
+	/**
+	 * Add a GROUP BY statement
+	 */
+	public Q groupBy(String fieldName) {
+		this.groupBy.add(fieldName);
+		return this;
+	}
+
+	/**
+	 * Add a GROUP BY statement
+	 */
+	public Q groupBy(Set<String> fieldNames) {
+		this.groupBy.addAll(fieldNames);
+		return this;
+	}
+
 	/**
 	 * Add a LIMIT statement
 	 */
@@ -125,6 +142,17 @@ public class Q {
 		}
 	}
 
+	/**
+	 * Build the GROUP BY statement
+	 */
+	public String buildGroupBy() {
+		if (!this.groupBy.isEmpty()) {
+			return 'GROUP BY ' + String.join(new List<String>(this.groupBy), ', ');
+		} else {
+			return null;
+		}
+	}
+
 	/**
 	 * Build the ORDER BY statement
 	 */
@@ -160,6 +188,10 @@ public class Q {
 			queryParts.add(this.buildOrderBy());
 		}
 
+		if (!this.groupBy.isEmpty()) {
+			queryParts.add(this.buildGroupBy());
+		}
+
 		if (this.numberOfRows != null) {
 			queryParts.add('LIMIT ' + this.numberOfRows);
 		}

force-app/main/default/classes/QTest.cls

@@ -105,4 +105,28 @@ private class QTest {
 		Database.query(query);
 	}
 
+	@isTest
+	static void testGroupBy() {
+		String query =
+			new Q(Lead.SObjectType)
+        .selectFields(new Set<String>{'LeadSource', 'COUNT(Name)'})
+				.groupBy('LeadSource')
+				.build();
+
+		System.assertEquals('SELECT LeadSource, COUNT(Name) FROM Lead GROUP BY LeadSource', query);
+		Database.query(query);
+	}
+
+	@isTest
+	static void testGroupByMultiple() {
+		String query =
+			new Q(Lead.SObjectType)
+        .selectFields(new Set<String>{'Status', 'LeadSource', 'COUNT(Name)'})
+				.groupBy(new Set<String>{'Status', 'LeadSource'})
+				.build();
+
+		System.assertEquals('SELECT Status, LeadSource, COUNT(Name) FROM Lead GROUP BY Status, LeadSource', query);
+		Database.query(query);
+	}
+
 }