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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '355664a304353d007b6a4f9e732604cf704f434502c65f1a444ab3e770a3aec1' 
  AND token = '+EXyQbMCaR+ptzXB3z8kgikNoJMqw3YB+kp+NpT4j6w=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00025

JSON explain

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