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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '508303ab51ca576c258e12ad38d2339dc4f569cc3a4ed042d3755b1f429b647a' 
  AND token = 'oEAMLdAJY55hIykDEJSt5JurSfnDXgVCYosc3CXZWSw=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00027

JSON explain

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