SELECT 
  category_id, 
  parent_id 
FROM 
  csscart_categories 
WHERE 
  parent_id IN(
    235, 198, 176, 178, 190, 255, 182, 175, 
    197, 236, 185, 191, 193, 199, 240, 179, 
    186, 174, 234, 194, 200, 180, 238, 202, 
    187, 181, 195, 177, 237, 196, 188, 254, 
    189, 263
  ) 
  AND category_id != 264

Query time 0.00040

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "20.20"
    },
    "table": {
      "table_name": "csscart_categories",
      "access_type": "ALL",
      "possible_keys": [
        "PRIMARY",
        "parent",
        "p_category_id"
      ],
      "rows_examined_per_scan": 84,
      "rows_produced_per_join": 53,
      "filtered": "64.29",
      "cost_info": {
        "read_cost": "9.40",
        "eval_cost": "10.80",
        "prefix_cost": "20.20",
        "data_read_per_join": "140K"
      },
      "used_columns": [
        "category_id",
        "parent_id"
      ],
      "attached_condition": "((`demoecarter_pos`.`csscart_categories`.`parent_id` in (235,198,176,178,190,255,182,175,197,236,185,191,193,199,240,179,186,174,234,194,200,180,238,202,187,181,195,177,237,196,188,254,189,263)) and (`demoecarter_pos`.`csscart_categories`.`category_id` <> 264))"
    }
  }
}