Fix GROUPING SETS tuple unwrapping in EXPLAIN output

When outputting GROUPING SETS elements, unwrap tuple literals to output
their elements directly with correct child counts instead of wrapping
in ExpressionList(children 1) and outputting as Function tuple.

Fixes tests for GROUPING SETS queries across 12 test files.

Author: claude

internal/explain/select.go

@@ -102,8 +102,23 @@ func explainSelectQuery(sb *strings.Builder, n *ast.SelectQuery, indent string,
 		for _, g := range n.GroupBy {
 			if n.GroupingSets {
 				// Each grouping set is wrapped in an ExpressionList
-				fmt.Fprintf(sb, "%s  ExpressionList (children 1)\n", indent)
-				Node(sb, g, depth+3)
+				// but we need to unwrap tuples and output elements directly
+				if lit, ok := g.(*ast.Literal); ok && lit.Type == ast.LiteralTuple {
+					if elements, ok := lit.Value.([]ast.Expression); ok {
+						fmt.Fprintf(sb, "%s  ExpressionList (children %d)\n", indent, len(elements))
+						for _, elem := range elements {
+							Node(sb, elem, depth+3)
+						}
+					} else {
+						// Fallback for unexpected tuple value type
+						fmt.Fprintf(sb, "%s  ExpressionList (children 1)\n", indent)
+						Node(sb, g, depth+3)
+					}
+				} else {
+					// Single expression grouping set
+					fmt.Fprintf(sb, "%s  ExpressionList (children 1)\n", indent)
+					Node(sb, g, depth+3)
+				}
 			} else {
 				Node(sb, g, depth+2)
 			}

parser/testdata/01710_aggregate_projection_with_grouping_set/metadata.json

@@ -1,5 +1 @@
-{
-  "explain_todo": {
-    "stmt4": true
-  }
-}
+{}

parser/testdata/02304_grouping_set_order_by/metadata.json

@@ -1,5 +1 @@
-{
-  "explain_todo": {
-    "stmt1": true
-  }
-}
+{}

parser/testdata/02481_analyzer_optimize_grouping_sets_keys/metadata.json

@@ -1,7 +1 @@
-{
-  "explain_todo": {
-    "stmt4": true,
-    "stmt5": true,
-    "stmt6": true
-  }
-}
+{}

parser/testdata/02554_fix_grouping_sets_predicate_push_down/metadata.json

@@ -1,10 +1 @@
-{
-  "explain_todo": {
-    "stmt10": true,
-    "stmt13": true,
-    "stmt16": true,
-    "stmt17": true,
-    "stmt6": true,
-    "stmt9": true
-  }
-}
+{}

parser/testdata/02705_grouping_keys_equal_keys/metadata.json

@@ -1,5 +1 @@
-{
-  "explain_todo": {
-    "stmt1": true
-  }
-}
+{}

parser/testdata/03014_group_by_use_nulls_injective_functions_and_analyzer/metadata.json

@@ -1,7 +1 @@
-{
-  "explain_todo": {
-    "stmt2": true,
-    "stmt3": true,
-    "stmt4": true
-  }
-}
+{}

parser/testdata/03023_analyzer_optimize_group_by_function_keys_with_nulls/metadata.json

@@ -1,5 +1 @@
-{
-  "explain_todo": {
-    "stmt4": true
-  }
-}
+{}

parser/testdata/03150_grouping_sets_use_nulls_pushdown/metadata.json

@@ -1,10 +1 @@
-{
-  "explain_todo": {
-    "stmt10": true,
-    "stmt11": true,
-    "stmt5": true,
-    "stmt6": true,
-    "stmt7": true,
-    "stmt8": true
-  }
-}
+{}

parser/testdata/03168_cld2_tsan/metadata.json

@@ -1,5 +1 @@
-{
-  "explain_todo": {
-    "stmt1": true
-  }
-}
+{}