Fix migrations for SqlServer

src/Umbraco.Core/Persistence/SqlSyntax/SqlServerSyntaxProvider.cs

@@ -225,6 +225,17 @@ order by T.name, I.name");
 
         }
 
+        /// <inheritdoc />
+        public override string GetDefaultConstraint(IDatabase db, string tableName, string columnName)
+        {
+            return db.Fetch<string>(@"select con.[name] as [constraintName]
+from sys.default_constraints con
+join sys.columns col on con.object_id=col.default_object_id
+join sys.tables tbl on col.object_id=tbl.object_id
+where tbl.[name]=@0 and col.[name]=@1;", tableName, columnName)
+                       .FirstOrDefault() ?? string.Empty;
+        }
+
         public override bool DoesTableExist(IDatabase db, string tableName)
         {
             var result =
@@ -276,7 +287,7 @@ order by T.name, I.name");
             return null;
         }
 
-        public override string DeleteDefaultConstraint => "ALTER TABLE [{0}] DROP CONSTRAINT [DF_{0}_{1}]";
+        public override string DeleteDefaultConstraint => "ALTER TABLE {0} DROP CONSTRAINT {2}";
 
         public override string DropIndex => "DROP INDEX {0} ON {1}";