add group ba additions to SelectUtils

Author: wumpz

src/main/java/net/sf/jsqlparser/statement/select/PlainSelect.java

@@ -190,6 +190,13 @@ public void setGroupByColumnReferences(List<Expression> list) {
         groupByColumnReferences = list;
     }
 
+    public void addGroupByColumnReference(Expression expr) {
+        if (groupByColumnReferences == null) {
+            groupByColumnReferences = new ArrayList<Expression>();
+        }
+        groupByColumnReferences.add(expr);
+    }
+
     public OracleHierarchicalExpression getOracleHierarchical() {
         return oracleHierarchical;
     }
@@ -264,10 +271,10 @@ public String toString() {
                 sql.append(limit);
             }
             if (offset != null) {
-            	sql.append(offset);
+                sql.append(offset);
             }
             if (fetch != null) {
-            	sql.append(fetch);
+                sql.append(fetch);
             }
             if (isForUpdate()) {
                 sql.append(" FOR UPDATE");

src/main/java/net/sf/jsqlparser/util/SelectUtils.java

@@ -147,4 +147,29 @@ public static Join addJoin(Select select, final Table table, final Expression on
 		}
 		throw new UnsupportedOperationException("Not supported yet.");
 	}
+    
+    /**
+     * Adds group by to a plain select statement.
+     * @param select
+     * @param expr 
+     */
+    public static void addGroupBy(Select select, final Expression expr) {
+        select.getSelectBody().accept(new SelectVisitor() {
+
+			@Override
+			public void visit(PlainSelect plainSelect) {
+                plainSelect.addGroupByColumnReference(expr);
+			}
+
+			@Override
+			public void visit(SetOperationList setOpList) {
+				throw new UnsupportedOperationException("Not supported yet.");
+			}
+
+			@Override
+			public void visit(WithItem withItem) {
+				throw new UnsupportedOperationException("Not supported yet.");
+			}
+		});
+    }
 }

src/test/java/net/sf/jsqlparser/util/SelectUtilsTest.java

@@ -91,5 +91,12 @@ public void testBuildSelectFromTableAndParsedExpression() throws JSQLParserExcep
 
 		assertTrue(((SelectExpressionItem)((PlainSelect)select.getSelectBody()).getSelectItems().get(0)).getExpression() instanceof Addition);
 	}
+    
+    @Test
+    public void testBuildSelectFromTableWithGroupBy() {
+        Select select = SelectUtils.buildSelectFromTable(new Table("mytable"));
+        SelectUtils.addGroupBy(select, new Column("b"));
+        assertEquals("SELECT * FROM mytable GROUP BY b", select.toString());
+    }
 
 }