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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '5c5a40b9148680c502768e69d3340a6c510bcf236ae83f62c1a471841de26728' 
  AND token = '1khRgG74To3LLeP6GUMk/tMvIfKDgEldvmaEc9ymUK4=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00034

JSON explain

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