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SELECT 
  1 
FROM 
  cscart_multi_declock_keys 
WHERE 
  key_id = 'b961fc7c816722de6107034b079558c6b1882e8fcd0b8d774e3d5ebd59580768' 
  AND token = 'aVNrWlnRpfc7DKTl8kDSrdY615+csUUhbI9ThPC7jNI=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00033

JSON explain

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