diff --git a/django/db/backends/mysql/schema.py b/django/db/backends/mysql/schema.py
index df5f3b7fcdb..4efe008f427 100644
--- a/django/db/backends/mysql/schema.py
+++ b/django/db/backends/mysql/schema.py
@@ -30,11 +30,7 @@ class DatabaseSchemaEditor(BaseDatabaseSchemaEditor):
     def quote_value(self, value):
         # Inner import to allow module to fail to load gracefully
         import MySQLdb.converters
-
-        if isinstance(value, six.string_types):
-            return '"%s"' % six.text_type(value)
-        else:
-            return MySQLdb.escape(value, MySQLdb.converters.conversions)
+        return MySQLdb.escape(value, MySQLdb.converters.conversions)
 
     def skip_default(self, field):
         """
@@ -49,8 +45,7 @@ class DatabaseSchemaEditor(BaseDatabaseSchemaEditor):
         # Simulate the effect of a one-off default.
         if self.skip_default(field) and field.default not in {None, NOT_PROVIDED}:
             effective_default = self.effective_default(field)
-            self.execute('UPDATE %(table)s SET %(column)s=%(default)s' % {
+            self.execute('UPDATE %(table)s SET %(column)s = %%s' % {
                 'table': self.quote_name(model._meta.db_table),
                 'column': self.quote_name(field.column),
-                'default': self.quote_value(effective_default),
-            })
+            }, [effective_default])
diff --git a/django/db/backends/oracle/schema.py b/django/db/backends/oracle/schema.py
index 447c0a231fc..7843b96943e 100644
--- a/django/db/backends/oracle/schema.py
+++ b/django/db/backends/oracle/schema.py
@@ -1,5 +1,6 @@
 import copy
 import datetime
+import binascii
 
 from django.utils import six
 from django.db.backends.schema import BaseDatabaseSchemaEditor
@@ -21,7 +22,9 @@ class DatabaseSchemaEditor(BaseDatabaseSchemaEditor):
         if isinstance(value, (datetime.date, datetime.time, datetime.datetime)):
             return "'%s'" % value
         elif isinstance(value, six.string_types):
-            return repr(value)
+            return "'%s'" % six.text_type(value).replace("\'", "\'\'")
+        elif isinstance(value, buffer):
+            return "'%s'" % binascii.hexlify(value)
         elif isinstance(value, bool):
             return "1" if value else "0"
         else:
diff --git a/django/db/backends/sqlite3/schema.py b/django/db/backends/sqlite3/schema.py
index 07036885991..b7a945080dc 100644
--- a/django/db/backends/sqlite3/schema.py
+++ b/django/db/backends/sqlite3/schema.py
@@ -27,7 +27,7 @@ class DatabaseSchemaEditor(BaseDatabaseSchemaEditor):
         elif isinstance(value, six.integer_types):
             return str(value)
         elif isinstance(value, six.string_types):
-            return '"%s"' % six.text_type(value)
+            return "'%s'" % six.text_type(value).replace("\'", "\'\'")
         elif value is None:
             return "NULL"
         elif isinstance(value, (bytes, bytearray, six.memoryview)):