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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'd27ca0a786b8f3fba3340c5e3294f39f947bdc4e71322e5ea5c5b2b22347fa51' 
  AND token = 'dxJeMV4zYYFoUQ+UCyYH3jzJM3+A6iqBy5l3OSdpzmk=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00022

JSON explain

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