sql/analyzer/prune_columns.go: Turn off pruneColumns when a Subquery expression exists.

sql/analyzer/prune_columns.go

@@ -56,6 +56,11 @@ func pruneColumns(ctx *sql.Context, a *Analyzer, n sql.Node, scope *Scope) (sql.
 		return n, nil
 	}
 
+	if !pruneColumnsIsSafe(n) {
+		a.Log("not pruning columns because it is not safe.")
+		return n, nil
+	}
+
 	columns := columnsUsedByNode(n)
 	findUsedColumns(columns, n)
 
@@ -72,6 +77,20 @@ func pruneColumns(ctx *sql.Context, a *Analyzer, n sql.Node, scope *Scope) (sql.
 	return fixRemainingFieldsIndexes(n, scope)
 }
 
+func pruneColumnsIsSafe(n sql.Node) bool {
+	isSafe := true
+	// We do not run pruneColumns if there is a Subquery
+	// expression, because the field rewrites and scope handling
+	// in here are not principled.
+	plan.InspectExpressions(n, func(e sql.Expression) bool {
+		if _, ok := e.(*plan.Subquery); ok {
+			isSafe = false
+		}
+		return isSafe
+	})
+	return isSafe
+}
+
 func columnsUsedByNode(n sql.Node) usedColumns {
 	columns := make(usedColumns)
 

sql/analyzer/prune_columns_test.go

@@ -357,7 +357,7 @@ func TestPruneColumns(t *testing.T) {
 			),
 		},
 		{
-			name: "Drop projected columns not in subquery",
+			name: "Keep projected columns when there is a subquery",
 			node: plan.NewProject(
 				[]sql.Expression{
 					gf(0, "t1", "foo"),
@@ -405,6 +405,7 @@ func TestPruneColumns(t *testing.T) {
 				plan.NewProject(
 					[]sql.Expression{
 						gf(0, "t1", "foo"),
+						gf(1, "t1", "bar"),
 					},
 					plan.NewResolvedTable(t1),
 				),