ent: support schema view (#4157)

examples/viewcomposite/schema.sql

@@ -0,0 +1,13 @@
+-- Create "clean_users" view
+CREATE VIEW "clean_users" ("id", "name", "public_info") AS SELECT id,
+    name,
+    public_info
+   FROM users;
+
+-- Create "pet_user_names" view
+CREATE VIEW "pet_user_names" ("name") AS SELECT DISTINCT name
+   FROM ( SELECT users.name
+           FROM users
+        UNION
+         SELECT pets.name
+           FROM pets) all_names;