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SELECT 
  1 
FROM 
  cscart_multi_declock_keys 
WHERE 
  key_id = 'b0391f675979c1fc03dc9849716f587fd3ad298f3e2631840ba1a768ce19a7b5' 
  AND token = 'b8Uigjyyh8w1vzAi6pLbssLbNfDaglOb3rVTGzpoSDk=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00020

JSON explain

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