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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'a21d5558cac4aaa1da4931dcdfdc393334470c99c41594e94b0db68c4dc14137' 
  AND token = '+N3YZ75j3FjmHtt/RaOzRV+3oftpqV3vfWb/5mrEv3Y=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00035

JSON explain

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