Update optional-conditions.md

Author: rkrx

doc/optional-conditions.md

@@ -11,11 +11,17 @@ $filter = [
 	],
 ];
 
+$orderBy = [
+	['date', 'DESC'],  // Define the Sort-Order as a Multi-Value-Field
+	['name' => 'ASC'], // ... or define the Sort-Order as a Key-Value-Field
+];
+
 $query = $db
 ->from('t', 'test')
 ->where(new DBExprFilter('t.name = ?', $filter, 'name'))
 ->where(new DBExprFilter('t.date >= ?', $filter, 'date.start')) // Key in dot-notation
 ->where(new DBExprFilter('t.date <= ?', $filter, ['date', 'end'])) // Key in array-notation
+->orderBy(new DBExprOrderBySpec(['name', 'date' => 'DATE(t.date)'], $orderBy))
 ```
 
 You can also define validation rules to only match certain data in `$filter`.