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SELECT 
  1 
FROM 
  cscart_multi_declock_keys 
WHERE 
  key_id = 'f5588af0cd0c3efd778851c266dbdfb170ce256a521997d9df5d40ae3d9d347a' 
  AND token = 'O0BlHdAZKJLwweu+EbQPIcWx5xqBt0E7kCmQZ5cIsuY=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00044

JSON explain

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