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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '51cf0bebb47f05c02f827aedafc7a45f45882fbd3f5e1ce755a4350cbd024e24' 
  AND token = '6GxSRTbOSf7NmSfugFmjuaL6oa3B4ubz9xh2dgyzQUg=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00042

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "message": "Impossible WHERE noticed after reading const tables"
    }
  }
}