Drop constraint when is postgres

bank.py

@@ -33,25 +33,6 @@ class BankAccount(metaclass=PoolMeta):
     def search_companies(cls, name, clause):
         return [('bank.party.companies',) + tuple(clause[1:])]
 
-
-class BankAccountNumber(metaclass=PoolMeta):
-    __name__ = 'bank.account.number'
-
-    @classmethod
-    def __register__(cls, module_name):
-        cursor = Transaction().connection.cursor()
-
-        # since issue11198 fill or create bank from IBAN and enforce uniqueness
-        # replace default sql_constrain (keep same name) that always return false
-        exist = backend.TableHandler.table_exist(cls._table)
-        if exist:
-            cursor.execute("ALTER TABLE bank_account_number DROP CONSTRAINT "
-                "IF EXISTS bank_account_number_number_iban_exclude")
-            cursor.execute("ALTER table bank_account_number add constraint "
-                "bank_account_number_number_iban_exclude check (type != 'x')")
-
-        super(BankAccountNumber, cls).__register__(module_name)
-
     @classmethod
     def get_owners_by_companies(cls, records, name):
         PartyCompany = Pool().get('party.company.rel')
@@ -79,3 +60,22 @@ class BankAccountNumber(metaclass=PoolMeta):
     @classmethod
     def set_owners_by_companies(cls, records, name, value):
         cls.write(records, {'owners': value})
+
+
+class BankAccountNumber(metaclass=PoolMeta):
+    __name__ = 'bank.account.number'
+
+    @classmethod
+    def __register__(cls, module_name):
+        cursor = Transaction().connection.cursor()
+
+        # since issue11198 fill or create bank from IBAN and enforce uniqueness
+        # replace default sql_constrain (keep same name) that always return false
+        exist = backend.TableHandler.table_exist(cls._table)
+        if exist and backend.name == 'postgresql':
+            cursor.execute("ALTER TABLE bank_account_number DROP CONSTRAINT "
+                "IF EXISTS bank_account_number_number_iban_exclude")
+            cursor.execute("ALTER table bank_account_number add constraint "
+                "bank_account_number_number_iban_exclude check (type != 'x')")
+
+        super(BankAccountNumber, cls).__register__(module_name)