SELECT 
  city_name as location 
FROM 
  cscart_products_addition_info 
WHERE 
  product_id = 49794

Query time 0.01060

JSON explain

{
  "query_block": {
    "select_id": 1,
    "const_condition": "1",
    "nested_loop": [
      {
        "table": {
          "table_name": "cscart_products",
          "access_type": "const",
          "possible_keys": ["PRIMARY", "status"],
          "key": "PRIMARY",
          "key_length": "3",
          "used_key_parts": ["product_id"],
          "ref": ["const"],
          "rows": 1,
          "filtered": 100
        }
      },
      {
        "table": {
          "table_name": "cscart_companies",
          "access_type": "const",
          "possible_keys": ["PRIMARY"],
          "key": "PRIMARY",
          "key_length": "4",
          "used_key_parts": ["company_id"],
          "ref": ["const"],
          "rows": 1,
          "filtered": 100
        }
      },
      {
        "table": {
          "table_name": "cscart_products_categories",
          "access_type": "ref",
          "possible_keys": ["pt"],
          "key": "pt",
          "key_length": "3",
          "used_key_parts": ["product_id"],
          "ref": ["const"],
          "rows": 10,
          "filtered": 100,
          "using_index": true
        }
      },
      {
        "table": {
          "table_name": "CT",
          "access_type": "eq_ref",
          "possible_keys": ["PRIMARY"],
          "key": "PRIMARY",
          "key_length": "22",
          "used_key_parts": ["city_id"],
          "ref": ["const"],
          "rows": 1,
          "filtered": 100,
          "attached_condition": "trigcond(CT.city_id = <cache>(convert('79' using utf8mb4)))"
        }
      }
    ]
  }
}