SELECT 
  * 
FROM 
  cscart_products_categories 
WHERE 
  product_id = 1973

Query time 0.00051

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "24.00"
    },
    "table": {
      "table_name": "cscart_products_categories",
      "access_type": "ref",
      "possible_keys": [
        "pt"
      ],
      "key": "pt",
      "used_key_parts": [
        "product_id"
      ],
      "key_length": "3",
      "ref": [
        "const"
      ],
      "rows_examined_per_scan": 20,
      "rows_produced_per_join": 20,
      "filtered": "100.00",
      "cost_info": {
        "read_cost": "20.00",
        "eval_cost": "4.00",
        "prefix_cost": "24.00",
        "data_read_per_join": "320"
      },
      "used_columns": [
        "product_id",
        "category_id",
        "link_type",
        "position",
        "category_position"
      ]
    }
  }
}

Result

product_id category_id link_type position category_position
1973 337 A 0 10
1973 338 A 0 20
1973 339 A 0 30
1973 340 A 0 40
1973 349 A 0 50
1973 352 A 0 60
1973 359 A 0 70
1973 360 A 0 80
1973 362 A 0 90
1973 363 A 0 100
1973 368 A 0 110
1973 369 A 0 120
1973 370 A 0 130
1973 377 A 0 140
1973 379 A 0 150
1973 381 A 0 160
1973 361 M 0 0