SELECT 
  category_id, 
  parent_id 
FROM 
  cscart_categories 
WHERE 
  parent_id IN(
    7128, 7535, 7093, 7510, 7156, 7513, 7536, 
    7175, 7516, 7537, 7186, 7519, 7204, 
    7520, 7217, 7521, 7238, 7524, 7526, 
    7374, 7385, 7561, 7572, 7587, 7593, 
    7503, 7534
  )

Query time 0.00100

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "20.24"
    },
    "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": 48,
      "rows_produced_per_join": 48,
      "filtered": "100.00",
      "using_index": true,
      "cost_info": {
        "read_cost": "10.64",
        "eval_cost": "9.60",
        "prefix_cost": "20.24",
        "data_read_per_join": "284K"
      },
      "used_columns": [
        "category_id",
        "parent_id"
      ],
      "attached_condition": "(`webmarco`.`cscart_categories`.`parent_id` in (7128,7535,7093,7510,7156,7513,7536,7175,7516,7537,7186,7519,7204,7520,7217,7521,7238,7524,7526,7374,7385,7561,7572,7587,7593,7503,7534))"
    }
  }
}