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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'c21697993b4c9ddf1507bea28796f5d07b9bce07484dcdd237f5d1df0b6ce39a' 
  AND token = '4meNyx1dPsm60ndjwl984jvoGqt4EoWWcRynZb0xbR8=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00027

JSON explain

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