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SELECT 
  category_id, 
  parent_id 
FROM 
  jmj_categories 
WHERE 
  parent_id IN(8, 19, 25) 
  AND category_id != 1

Query time 0.01103

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "29.61"
    },
    "table": {
      "table_name": "jmj_categories",
      "access_type": "range",
      "possible_keys": [
        "PRIMARY",
        "parent",
        "p_category_id"
      ],
      "key": "parent",
      "used_key_parts": [
        "parent_id"
      ],
      "key_length": "3",
      "rows_examined_per_scan": 19,
      "rows_produced_per_join": 19,
      "filtered": "100.00",
      "index_condition": "(`jmj_test`.`jmj_categories`.`parent_id` in (8,19,25))",
      "cost_info": {
        "read_cost": "25.81",
        "eval_cost": "3.80",
        "prefix_cost": "29.61",
        "data_read_per_join": "73K"
      },
      "used_columns": [
        "category_id",
        "parent_id"
      ],
      "attached_condition": "(`jmj_test`.`jmj_categories`.`category_id` <> 1)"
    }
  }
}

Result

category_id	parent_id
9	8
10	8
11	8
12	8
13	8
14	8
15	8
16	8
18	8
17	8
20	19
21	19
22	19
23	19
24	19
26	25
30	25
27	25
28	25
29	25

category_id	parent_id
9	8
10	8
11	8
12	8
13	8
14	8
15	8
16	8
18	8
17	8
20	19
21	19
22	19
23	19
24	19
26	25
30	25
27	25
28	25
29	25

category_id	parent_id
9	8
10	8
11	8
12	8
13	8
14	8
15	8
16	8
18	8
17	8
20	19
21	19
22	19
23	19
24	19
26	25
30	25
27	25
28	25
29	25

category_id	parent_id
9	8
10	8
11	8
12	8
13	8
14	8
15	8
16	8
18	8
17	8
20	19
21	19
22	19
23	19
24	19
26	25
30	25
27	25
28	25
29	25