Fixes group by for more than 2 nested path expressions. (#461)

* Fixes group by for more than 2 nested path expressions.

* Renames test description and refines kdoc.

lang/src/org/partiql/lang/eval/visitors/GroupByPathExpressionVisitorTransform.kt

@@ -31,8 +31,9 @@ class GroupByPathExpressionVisitorTransform(
         /**
          * Determines if [gbi] is an expression of the type that should be replaced elsewhere in the query.
          *
-         * Since we are only concerned about SQL-92 compatibility here, we only replace path expressions that
-         * have a single component, i.e. `f.bar` but not `f.bar.bat`.  (The latter is not part of SQL-92.)
+         * As we support querying nested data, we are not just limited to SQL-92 compatibility (that have
+         * path expressions with single component, i.e. `foo.bar`) but also replace path expressions that
+         * have more than one component, i.e. `f.bar.bat`.
          */
         fun canBeSubstituted(groupKey: PartiqlAst.GroupKey): Boolean {
             val expr = groupKey.expr
@@ -42,15 +43,12 @@ class GroupByPathExpressionVisitorTransform(
             return when {
                 asName == null                                     -> throw IllegalStateException("GroupByItem.asName must be specified for this transform to work")
                 !asName.metas.containsKey(IsSyntheticNameMeta.TAG) ->
-                    // If this meta is not present it would indicate that the alias was explicitly specifed, which is
+                    // If this meta is not present it would indicate that the alias was explicitly specified, which is
                     // not allowed by SQL-92, so ignore.
                     false
 
                 // Group by expressions other than paths aren't part of SQL-92 so ignore
                 expr !is PartiqlAst.Expr.Path                      -> false
-
-                // Path expressions containing more than one component (i.e. `one.two.three`) are also not part of SQL-92
-                expr.steps.size != 1                               -> false
                 else                                               -> true
             }
 

lang/test/org/partiql/lang/eval/EvaluatingCompilerGroupByTest.kt

@@ -77,7 +77,13 @@ EvaluatingCompilerGroupByTest : EvaluatorTestBase() {
             { customerId: 789, sellerId: 2, productId: 88888, cost: 8 },
             { customerId: 789, sellerId: 1, productId: 99999, cost: 9 },
             { customerId: 100, sellerId: 2, productId: 10000, cost: 10 }
-        ]""").toSession()
+        ]""",
+        "employees" to """[
+             { name: 'Joey', age: 25, manager: { name: 'John', address: { city: 'Seattle' } } },
+             { name: 'Chandler', age: 27, manager: { name: 'Rocky', address: { city: 'Seattle' } } },
+             { name: 'Ross', age: 22, manager: { 'name': 'Alex', address: { city: 'Chicago' } } }
+        ]"""
+     ).toSession()
 
     companion object {
 
@@ -720,7 +726,11 @@ EvaluatingCompilerGroupByTest : EvaluatorTestBase() {
         EvaluatorTestCase(
             "SELECT VALUE with nested aggregates",
             "SELECT VALUE (SELECT SUM(outerFromSource.col1) AS the_sum FROM <<1>>) FROM simple_1_col_1_group as outerFromSource",
-            "<< << { 'the_sum': 1 } >>,  << { 'the_sum': 1 } >> >>")
+            "<< << { 'the_sum': 1 } >>,  << { 'the_sum': 1 } >> >>"),
+        EvaluatorTestCase(
+            "SELECT with GROUP BY path expression having more than 1 component.",
+            "SELECT avg(age) as avg_employee_age, manager.address.city FROM employees GROUP BY manager.address.city",
+            "<<{'avg_employee_age': 22, 'city': 'Chicago'}, {'avg_employee_age': 26, 'city': 'Seattle'}>>")
     )
 
     @Test