SELECT 
  products.product_id 
FROM 
  cscart_products as products 
  LEFT JOIN cscart_products_categories as products_categories ON products.product_id = products_categories.product_id 
WHERE 
  products.product_id = 2642 
  AND 1 
  AND products_categories.category_id IN (
    1186, 3107, 2438, 2453, 2463, 2494, 2676
  )

Query time 0.00025

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "0.68"
    },
    "nested_loop": [
      {
        "table": {
          "table_name": "products",
          "access_type": "const",
          "possible_keys": [
            "PRIMARY"
          ],
          "key": "PRIMARY",
          "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": "0.00",
            "eval_cost": "0.10",
            "prefix_cost": "0.00",
            "data_read_per_join": "5K"
          },
          "used_columns": [
            "product_id"
          ]
        }
      },
      {
        "table": {
          "table_name": "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": 0,
          "filtered": "50.00",
          "using_index": true,
          "cost_info": {
            "read_cost": "0.59",
            "eval_cost": "0.05",
            "prefix_cost": "0.69",
            "data_read_per_join": "8"
          },
          "used_columns": [
            "product_id",
            "category_id"
          ],
          "attached_condition": "(`cscart_db`.`products_categories`.`category_id` in (1186,3107,2438,2453,2463,2494,2676))"
        }
      }
    ]
  }
}