[#1665] Add support for the empty GROUP BY () clause

jOOQ-test/src/org/jooq/test/_/testcases/GroupByTests.java

@@ -47,6 +47,7 @@ import static org.jooq.impl.Factory.groupingId;
 import static org.jooq.impl.Factory.groupingSets;
 import static org.jooq.impl.Factory.one;
 import static org.jooq.impl.Factory.rollup;
+import static org.jooq.impl.Factory.trueCondition;
 
 import java.util.Arrays;
 
@@ -90,6 +91,19 @@ extends BaseTest<A, AP, B, S, B2S, BS, L, X, DATE, BOOL, D, T, U, I, IPK, T658,
     @Test
     public void testGrouping() throws Exception {
 
+        // [#1665] Test the empty GROUP BY clause
+        assertEquals(1, (int) create().selectOne()
+                                      .from(TBook())
+                                      .groupBy()
+                                      .fetchOne(0, Integer.class));
+
+        // [#1665] Test the empty GROUP BY clause
+        assertEquals(1, (int) create().selectOne()
+                                      .from(TBook())
+                                      .groupBy()
+                                      .having(trueCondition())
+                                      .fetchOne(0, Integer.class));
+
         // Test a simple group by query
         Field<Integer> count = count().as("c");
         Result<Record> result = create()

jOOQ-website/src/main/resources/manual-2.5.xml

@@ -1341,6 +1341,20 @@ GROUP BY AUTHOR_ID]]></sql>
 												This will return an arbitrary title per author. jOOQ supports this syntax, as jOOQ is not doing any checks internally, about the consistence of tables/fields/functions that you provide it.
 											</p>
 
+											<h3>Empty GROUP BY clauses</h3>
+											<p>
+												jOOQ supports empty <code>GROUP BY ()</code> clauses as well. This will result in <reference id="select-statement" title="SELECT statements"/> that return only one record.
+											</p>
+
+<code-pair>
+<sql><![CDATA[SELECT COUNT(*)
+FROM BOOK
+GROUP BY ()]]></sql>
+<java><![CDATA[create.selectCount()
+      .from(BOOK)
+      .groupBy();]]></java></code-pair>
+
+											
 											<h3>ROLLUP(), CUBE() and GROUPING SETS()</h3>
 											<p>
 												Some databases support the SQL standard grouping functions and some extensions thereof. See the manual's section about <reference id="grouping-functions" title="grouping functions"/> for more details.

jOOQ/src/main/java/org/jooq/SelectGroupByStep.java

@@ -83,12 +83,18 @@ public interface SelectGroupByStep extends SelectHavingStep {
 
     /**
      * Add a <code>GROUP BY</code> clause to the query
+     * <p>
+     * Calling this with an empty argument list will result in an empty
+     * <code>GROUP BY ()</code> clause being rendered.
      */
     @Support
     SelectHavingStep groupBy(Field<?>... fields);
 
     /**
      * Add a <code>GROUP BY</code> clause to the query
+     * <p>
+     * Calling this with an empty argument list will result in an empty
+     * <code>GROUP BY ()</code> clause being rendered.
      */
     @Support
     SelectHavingStep groupBy(Collection<? extends Field<?>> fields);

jOOQ/src/main/java/org/jooq/SelectQuery.java

@@ -187,6 +187,9 @@ public interface SelectQuery extends Select<Record>, ConditionProvider, OrderPro
 
     /**
      * Adds grouping fields
+     * <p>
+     * Calling this with an empty argument list will result in an empty
+     * <code>GROUP BY ()</code> clause being rendered.
      *
      * @param fields The grouping fields
      */
@@ -195,6 +198,9 @@ public interface SelectQuery extends Select<Record>, ConditionProvider, OrderPro
 
     /**
      * Adds grouping fields
+     * <p>
+     * Calling this with an empty argument list will result in an empty
+     * <code>GROUP BY ()</code> clause being rendered.
      *
      * @param fields The grouping fields
      */

jOOQ/src/main/java/org/jooq/impl/AbstractSubSelect.java

@@ -96,14 +96,13 @@ implements
     private final ConditionProviderImpl connectBy;
     private boolean                     connectByNoCycle;
     private final ConditionProviderImpl connectByStartWith;
+    private boolean                     grouping;
     private final FieldList             groupBy;
     private final ConditionProviderImpl having;
     private final SortFieldList         orderBy;
     private boolean                     orderBySiblings;
     private final Limit                 limit;
 
-
-
     AbstractSubSelect(Configuration configuration) {
         this(configuration, null);
     }
@@ -506,10 +505,17 @@ implements
 
         // GROUP BY and HAVING clause
         // --------------------------
-        if (!getGroupBy().isEmpty()) {
+        if (grouping) {
             context.formatSeparator()
-                   .keyword("group by ")
-                   .sql(getGroupBy());
+                   .keyword("group by ");
+
+            // [#1665] Empty GROUP BY () clauses need parentheses
+            if (getGroupBy().isEmpty()) {
+                context.sql("()");
+            }
+            else {
+                context.sql(getGroupBy());
+            }
         }
 
         if (!(getHaving().getWhere() instanceof TrueCondition)) {
@@ -724,6 +730,10 @@ implements
         return from;
     }
 
+    final void setGrouping() {
+        grouping = true;
+    }
+
     final FieldList getGroupBy() {
         return groupBy;
     }

jOOQ/src/main/java/org/jooq/impl/SelectQueryImpl.java

@@ -105,6 +105,7 @@ class SelectQueryImpl extends AbstractSubSelect<Record> implements SelectQuery {
 
     @Override
     public final void addGroupBy(Collection<? extends Field<?>> fields) {
+        setGrouping();
         getGroupBy().addAll(fields);
     }
 

jOOQ/src/test/java/org/jooq/test/jOOQTest.java

@@ -1884,6 +1884,11 @@ public class jOOQTest {
         SelectQuery q = create.selectQuery();
         q.addFrom(TABLE1);
 
+        q.addGroupBy();
+        assertEquals("select \"TABLE1\".\"ID1\", \"TABLE1\".\"NAME1\", \"TABLE1\".\"DATE1\" from \"TABLE1\" group by ()", r_refI().render(q));
+        assertEquals("select \"TABLE1\".\"ID1\", \"TABLE1\".\"NAME1\", \"TABLE1\".\"DATE1\" from \"TABLE1\" group by ()", r_ref().render(q));
+        assertEquals(q, create.select().from(TABLE1).groupBy());
+
         q.addGroupBy(FIELD_ID1);
         assertEquals("select \"TABLE1\".\"ID1\", \"TABLE1\".\"NAME1\", \"TABLE1\".\"DATE1\" from \"TABLE1\" group by \"TABLE1\".\"ID1\"", r_refI().render(q));
         assertEquals("select \"TABLE1\".\"ID1\", \"TABLE1\".\"NAME1\", \"TABLE1\".\"DATE1\" from \"TABLE1\" group by \"TABLE1\".\"ID1\"", r_ref().render(q));