SELECT 
  category_id, 
  parent_id 
FROM 
  cscart_categories 
WHERE 
  parent_id IN(
    344, 372, 395, 365, 388, 312, 348, 287, 
    324, 288, 389, 373, 313, 366, 345, 340, 
    349, 325, 334, 367, 390, 289, 350, 346, 
    314, 341, 374, 351, 375, 368, 315, 290, 
    391, 347, 326, 342, 376, 369, 392, 316, 
    291, 393, 292, 377, 329, 387, 294, 394, 
    318, 330, 295, 317, 293, 296, 266, 268, 
    343, 286, 364, 371, 396, 397, 398, 399
  )

Query time 0.00069

JSON explain

{
  "query_block": {
    "select_id": 1,
    "nested_loop": [
      {
        "table": {
          "table_name": "cscart_categories",
          "access_type": "ALL",
          "possible_keys": ["parent"],
          "rows": 70,
          "filtered": 100,
          "attached_condition": "cscart_categories.parent_id in (344,372,395,365,388,312,348,287,324,288,389,373,313,366,345,340,349,325,334,367,390,289,350,346,314,341,374,351,375,368,315,290,391,347,326,342,376,369,392,316,291,393,292,377,329,387,294,394,318,330,295,317,293,296,266,268,343,286,364,371,396,397,398,399)"
        }
      }
    ]
  }
}