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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '421a64f249069e1fa8e0586163d1c99642fd80b16bb6402360341bfbe518d981' 
  AND token = '6XUy+mzkADPjZJWgtPyUs1fZ+oRuw9N+HCSkzmkgd3Q=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00035

JSON explain

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