SELECT 
  category_id, 
  parent_id 
FROM 
  cscart_categories 
WHERE 
  parent_id IN(
    311, 314, 312, 315, 313, 318, 297, 302, 
    303, 306
  ) 
  AND category_id != 264

Query time 0.00020

JSON explain

{
  "query_block": {
    "select_id": 1,
    "nested_loop": [
      {
        "table": {
          "table_name": "cscart_categories",
          "access_type": "ALL",
          "possible_keys": ["PRIMARY", "parent", "p_category_id"],
          "rows": 11,
          "filtered": 100,
          "attached_condition": "cscart_categories.parent_id in (311,314,312,315,313,318,297,302,303,306) and cscart_categories.category_id <> 264"
        }
      }
    ]
  }
}