SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '68acd1403f2a07a4bb110e856fcfaf938154a401f304e26fdd6729dc750b666a' 
  AND token = 'ApPMKiZhiQmvWFevNXKUY3AeHgB6vCbL9kYpM/1MBsw=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00022

JSON explain

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