SELECT 
  * 
FROM 
  tconnect_companies AS com 
  LEFT JOIN tconnect_products AS prod ON com.company_id = prod.company_id 
WHERE 
  prod.product_id = 242

Query time 0.00139

JSON explain

{
  "query_block": {
    "select_id": 1,
    "nested_loop": [
      {
        "table": {
          "table_name": "prod",
          "access_type": "const",
          "possible_keys": ["PRIMARY"],
          "key": "PRIMARY",
          "key_length": "3",
          "used_key_parts": ["product_id"],
          "ref": ["const"],
          "rows": 1,
          "filtered": 100
        }
      },
      {
        "table": {
          "table_name": "com",
          "access_type": "const",
          "possible_keys": ["PRIMARY"],
          "key": "PRIMARY",
          "key_length": "4",
          "used_key_parts": ["company_id"],
          "ref": ["const"],
          "rows": 1,
          "filtered": 100
        }
      }
    ]
  }
}