SELECT 
  category_id, 
  parent_id 
FROM 
  cscart_categories 
WHERE 
  parent_id IN(
    7918, 8001, 7971, 8060, 8023, 8078, 7972, 
    7919, 8002, 8061, 8024, 8079, 7973, 
    7920, 8062, 8025, 8003, 8080, 7974, 
    7921, 8026, 8004, 8081, 8063, 7975, 
    7922, 8027, 8005, 8082, 7923, 8028, 
    8083, 8006, 7924, 8029, 8084, 8007, 
    7925, 8030, 8085, 7926, 7927, 7928, 
    7929, 7930, 7931, 7932, 7933, 7934, 
    7935, 7936, 7937, 7938, 7939, 7940, 
    7941, 7942
  )

Query time 0.00078

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "34.67"
    },
    "table": {
      "table_name": "cscart_categories",
      "access_type": "range",
      "possible_keys": [
        "parent"
      ],
      "key": "parent",
      "used_key_parts": [
        "parent_id"
      ],
      "key_length": "3",
      "rows_examined_per_scan": 84,
      "rows_produced_per_join": 84,
      "filtered": "100.00",
      "using_index": true,
      "cost_info": {
        "read_cost": "17.87",
        "eval_cost": "16.80",
        "prefix_cost": "34.67",
        "data_read_per_join": "498K"
      },
      "used_columns": [
        "category_id",
        "parent_id"
      ],
      "attached_condition": "(`webmarco`.`cscart_categories`.`parent_id` in (7918,8001,7971,8060,8023,8078,7972,7919,8002,8061,8024,8079,7973,7920,8062,8025,8003,8080,7974,7921,8026,8004,8081,8063,7975,7922,8027,8005,8082,7923,8028,8083,8006,7924,8029,8084,8007,7925,8030,8085,7926,7927,7928,7929,7930,7931,7932,7933,7934,7935,7936,7937,7938,7939,7940,7941,7942))"
    }
  }
}