fix syntax error bug when setting default value

Author: milmazz

integration_test/sql/migration.exs

@@ -53,6 +53,9 @@ defmodule Ecto.Integration.MigrationTest do
 
         add :from_default_to_no_default, :integer, default: 0
         add :from_no_default_to_default, :integer
+
+        add :another_from_default_to_no_default, :integer, default: 0
+        add :another_from_no_default_to_default, :integer
       end
 
       alter table(:alter_col_migration) do
@@ -62,6 +65,9 @@ defmodule Ecto.Integration.MigrationTest do
 
         modify :from_default_to_no_default, :integer, default: nil
         modify :from_no_default_to_default, :integer, default: 0
+
+        modify :another_from_default_to_no_default, :integer, default: nil, from: {:integer, default: 0}
+        modify :another_from_no_default_to_default, :integer, default: 0, from: {:integer, default: nil}
       end
 
       execute "INSERT INTO alter_col_migration (from_null_to_not_null, another_from_null_to_not_null) VALUES ('foo', 'baz')"
@@ -143,7 +149,7 @@ defmodule Ecto.Integration.MigrationTest do
       end
 
       alter table(:alter_fk_comments) do
-        modify :alter_fk_user_id, references(:alter_fk_users, on_delete: :delete_all), from: references(:alter_fk_users, on_delete: :nothing)
+        modify :alter_fk_user_id, references(:alter_fk_users, on_delete: :nilify_all), from: references(:alter_fk_users, on_delete: :nothing)
       end
     end
 
@@ -566,12 +572,16 @@ defmodule Ecto.Integration.MigrationTest do
 
     assert ["foo"] ==
            PoolRepo.all from p in "alter_col_migration", select: p.from_null_to_not_null
+    assert ["baz"] ==
+           PoolRepo.all from p in "alter_col_migration", select: p.another_from_null_to_not_null
     assert [nil] ==
            PoolRepo.all from p in "alter_col_migration", select: p.from_not_null_to_null
     assert [nil] ==
            PoolRepo.all from p in "alter_col_migration", select: p.from_default_to_no_default
+    assert [nil] ==
+           PoolRepo.all from p in "alter_col_migration", select: p.another_from_default_to_no_default
     assert [0] ==
-           PoolRepo.all from p in "alter_col_migration", select: p.from_no_default_to_default
+           PoolRepo.all from p in "alter_col_migration", select: p.another_from_no_default_to_default
 
     query = "INSERT INTO `alter_col_migration` (\"from_not_null_to_null\") VALUES ('foo')"
     assert catch_error(PoolRepo.query!(query))
@@ -607,8 +617,10 @@ defmodule Ecto.Integration.MigrationTest do
     assert [id] = PoolRepo.all from p in "alter_fk_users", select: p.id
 
     PoolRepo.insert_all("alter_fk_posts", [[alter_fk_user_id: id]])
+    PoolRepo.insert_all("alter_fk_comments", [[alter_fk_user_id: id]])
     PoolRepo.delete_all("alter_fk_users")
     assert [nil] == PoolRepo.all from p in "alter_fk_posts", select: p.alter_fk_user_id
+    assert [nil] == PoolRepo.all from p in "alter_fk_comments", select: p.alter_fk_user_id
 
     :ok = down(PoolRepo, num, AlterForeignKeyOnDeleteMigration, log: false)
   end

lib/ecto/adapters/postgres/connection.ex

@@ -1582,18 +1582,25 @@ if Code.ensure_loaded?(Postgrex) do
       from_column_type = extract_column_type(opts[:from])
 
       drop_reference_expr = drop_reference_expr(opts[:from], table, name)
-      prefix_with_comma? = drop_reference_expr != []
+      any_drop_ref? = drop_reference_expr != []
 
       if column_type == column_type(from_column_type, opts) do
+        modify_null = modify_null(name, Keyword.put(opts, :prefix_with_comma, any_drop_ref?))
+        any_modify_null? = modify_null != []
+
         [
           drop_reference_expr,
-          modify_null(name, Keyword.put(opts, :prefix_with_comma, prefix_with_comma?)),
-          modify_default(name, type, opts)
+          modify_null,
+          modify_default(
+            name,
+            type,
+            Keyword.put(opts, :prefix_with_comma, any_drop_ref? or any_modify_null?)
+          )
         ]
       else
         [
           drop_reference_expr,
-          (prefix_with_comma? && ", ") || "",
+          (any_drop_ref? && ", ") || "",
           "ALTER COLUMN ",
           quote_name(name),
           " TYPE ",