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SELECT 
  cscart_users.* 
FROM 
  cscart_users 
WHERE 
  user_id = 101

Query time 0.00074

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "cscart_users",
      "access_type": "const",
      "possible_keys": ["PRIMARY"],
      "key": "PRIMARY",
      "key_length": "3",
      "used_key_parts": ["user_id"],
      "ref": ["const"],
      "rows": 1,
      "filtered": 100
    }
  }
}

Result

user_id	status	user_type	user_login	referer	is_root	company_id	last_login	last_activity	timestamp	password	salt	firstname	lastname	company	email	phone	fax	url	tax_exempt	lang_code	birthday	purchase_timestamp_from	purchase_timestamp_to	responsible_email	password_change_timestamp	api_key	helpdesk_user_id	storefront_id	janrain_identifier
101	A	V	TiHbKaH2		Y	27	1775473944	1775481363	1732995686	$2y$10$.xSqzwRtYf7OzrnTIJ3t.uu5N/WEn/JXiEGbC4ybFrX6xOj/I1jZ.		TiHbKaH2			xxxmaevkostantinxxx@gmail.com				N	en	0	0	0		1739750451		0	0