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SELECT 
  1 
FROM 
  cscart_multi_declock_keys 
WHERE 
  key_id = '521642d991569a614e14a213bc6512df75247002697079e63aa5caccb07de9ea' 
  AND token = '6u0SWUPHUBYo3XtWLZTUp+9ADtOgCHZTzHt3xM7PW+8=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00042

JSON explain

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