SELECT 
  category_id, 
  parent_id 
FROM 
  categories 
WHERE 
  parent_id IN(
    19316, 19319, 19320, 19318, 10337, 10339, 
    19339
  )

Query time 0.00044

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "2.67"
    },
    "table": {
      "table_name": "categories",
      "access_type": "range",
      "possible_keys": [
        "parent"
      ],
      "key": "parent",
      "used_key_parts": [
        "parent_id"
      ],
      "key_length": "3",
      "rows_examined_per_scan": 10,
      "rows_produced_per_join": 10,
      "filtered": "100.00",
      "using_index": true,
      "cost_info": {
        "read_cost": "1.67",
        "eval_cost": "1.00",
        "prefix_cost": "2.67",
        "data_read_per_join": "26K"
      },
      "used_columns": [
        "category_id",
        "parent_id"
      ],
      "attached_condition": "(`goimagine`.`categories`.`parent_id` in (19316,19319,19320,19318,10337,10339,19339))"
    }
  }
}