[CALCITE-1873] In a "GROUP BY ordinal" query, validator gives invalid…

… "Expression is not being grouped" error if column has alias

The solution is to ignore column aliases when validating a "GROUP BY
ordinal" query. Otherwise, you get an error like "Expression 'EMP.EMPNO'
is not being grouped" (see test case).

Close #490

core/src/main/java/org/apache/calcite/sql/validate/SqlValidatorImpl.java

@@ -5415,7 +5415,7 @@ public SqlNode visit(SqlLiteral literal) {
 
             // SQL ordinals are 1-based, but Sort's are 0-based
             int ordinal = intValue - 1;
-            return select.getSelectList().get(ordinal);
+            return SqlUtil.stripAs(select.getSelectList().get(ordinal));
           }
           break;
         }

core/src/test/java/org/apache/calcite/test/SqlValidatorTest.java

@@ -6304,6 +6304,12 @@ public boolean isBangEqualAllowed() {
         + " group by 1,2")
         .tester(strict).fails("Expression 'DEPTNO' is not being grouped")
         .tester(lenient).sansCarets().ok();
+    sql("select ^empno^, count(*) from emp group by 1 order by 1")
+        .tester(strict).fails("Expression 'EMPNO' is not being grouped")
+        .tester(lenient).sansCarets().ok();
+    sql("select ^empno^ eno, count(*) from emp group by 1 order by 1")
+        .tester(strict).fails("Expression 'EMPNO' is not being grouped")
+        .tester(lenient).sansCarets().ok();
     sql("select count(*) from (select 1 from emp"
         + " group by substring(ename from 2 for 3))")
         .tester(strict).ok()