SQL: [Tests] add tests for literals and GROUP BY

Add unit and integration tests where literals are SELECTed
in combination with GROUP BY and possibly aggregate functions.

Relates to elastic#41411 and elastic#34583
which have been fixed.

Author: matriv

x-pack/plugin/sql/qa/src/main/resources/agg.sql-spec

@@ -559,3 +559,9 @@ aggMultiWithHavingUsingInAndNullHandling
 SELECT MIN(salary) min, MAX(salary) max, gender g, COUNT(*) c FROM "test_emp" WHERE languages > 0 GROUP BY g HAVING max IN(74999, null, 74600) ORDER BY gender;
 aggMultiGroupByMultiWithHavingUsingInAndNullHandling
 SELECT MIN(salary) min, MAX(salary) max, gender g, languages l, COUNT(*) c FROM "test_emp" WHERE languages > 0 GROUP BY g, languages HAVING max IN (74500, null, 74600) ORDER BY gender, languages;
+
+// group by with literal
+implicitGroupByWithLiteral
+SELECT 10, MAX("salary") FROM test_emp;
+groupByWithLiteralAndCount
+SELECT 20, COUNT(*) from test_emp GROUP BY gender ORDER BY 2;

x-pack/plugin/sql/src/test/java/org/elasticsearch/xpack/sql/planner/QueryFolderTests.java

@@ -371,6 +371,24 @@ public void testGroupKeyTypes_DateTime() {
         assertThat(ee.output().get(1).toString(), startsWith("a{r}"));
     }
 
+    public void testSelectLiteralWithGroupBy() {
+        PhysicalPlan p = plan("SELECT 1, MAX(int) FROM test");
+        assertEquals(EsQueryExec.class, p.getClass());
+        EsQueryExec ee = (EsQueryExec) p;
+        assertEquals(2, ee.output().size());
+        assertEquals(Arrays.asList("1", "MAX(int)"), Expressions.names(ee.output()));
+        assertThat(ee.queryContainer().aggs().asAggBuilder().toString().replaceAll("\\s+", ""),
+                containsString("\"max\":{\"field\":\"int\""));
+
+        p = plan("SELECT 1, count(*) FROM test GROUP BY int");
+        assertEquals(EsQueryExec.class, p.getClass());
+        ee = (EsQueryExec) p;
+        assertEquals(2, ee.output().size());
+        assertEquals(Arrays.asList("1", "count(*)"), Expressions.names(ee.output()));
+        assertThat(ee.queryContainer().aggs().asAggBuilder().toString().replaceAll("\\s+", ""),
+                containsString("\"terms\":{\"field\":\"int\""));
+    }
+
     public void testConcatIsNotFoldedForNull() {
         PhysicalPlan p = plan("SELECT keyword FROM test WHERE CONCAT(keyword, null) IS NULL");
         assertEquals(LocalExec.class, p.getClass());