SELECT 
  cscart_products_categories.product_id, 
  cscart_products_categories.link_type, 
  cscart_categories.id_path 
FROM 
  cscart_categories 
  INNER JOIN cscart_products_categories ON cscart_products_categories.category_id = cscart_categories.category_id 
WHERE 
  cscart_products_categories.product_id IN (91764)

Query time 0.00032

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "0.70"
    },
    "nested_loop": [
      {
        "table": {
          "table_name": "cscart_products_categories",
          "access_type": "ref",
          "possible_keys": [
            "PRIMARY",
            "pt"
          ],
          "key": "pt",
          "used_key_parts": [
            "product_id"
          ],
          "key_length": "3",
          "ref": [
            "const"
          ],
          "rows_examined_per_scan": 1,
          "rows_produced_per_join": 1,
          "filtered": "100.00",
          "using_index": true,
          "cost_info": {
            "read_cost": "0.25",
            "eval_cost": "0.10",
            "prefix_cost": "0.35",
            "data_read_per_join": "16"
          },
          "used_columns": [
            "product_id",
            "category_id",
            "link_type"
          ]
        }
      },
      {
        "table": {
          "table_name": "cscart_categories",
          "access_type": "eq_ref",
          "possible_keys": [
            "PRIMARY",
            "p_category_id"
          ],
          "key": "PRIMARY",
          "used_key_parts": [
            "category_id"
          ],
          "key_length": "3",
          "ref": [
            "nuie_scalesta_net.cscart_products_categories.category_id"
          ],
          "rows_examined_per_scan": 1,
          "rows_produced_per_join": 1,
          "filtered": "100.00",
          "cost_info": {
            "read_cost": "0.25",
            "eval_cost": "0.10",
            "prefix_cost": "0.70",
            "data_read_per_join": "2K"
          },
          "used_columns": [
            "category_id",
            "id_path"
          ]
        }
      }
    ]
  }
}