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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'ab875dc564ffc70ac4d75a2fdde9b51057df1733e436fd7ca89f3c1f9c3e0fb6' 
  AND token = 'joTvLqWPZ9gYKHOYOUQY0pOATZT/dLtoKoss3RLwUoE=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00020

JSON explain

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