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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '355791c1b954f82a9d59710023fe3f53a40ab039d9bf4c013c6a639d73fb7441' 
  AND token = 'kPRQowddAflRc+jTkmem08dCOmQEui8TW9Ja95kZmHM=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00021

JSON explain

{
  "query_block": {
    "select_id": 1,
    "message": "no matching row in const table"
  }
}