SELECT 
  category_id, 
  parent_id 
FROM 
  cscart_categories 
WHERE 
  parent_id IN(
    242, 246, 229, 247, 243, 230, 249, 231, 
    244, 248, 232, 259, 228, 241, 245, 261
  ) 
  AND category_id != 265

Query time 0.00049

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": 90,
          "filtered": 28.88888931,
          "attached_condition": "cscart_categories.parent_id in (242,246,229,247,243,230,249,231,244,248,232,259,228,241,245,261) and cscart_categories.category_id <> 265"
        }
      }
    ]
  }
}