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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '1838a8528ad5d28e04669595b8a892885193c46204973a408c367a6e975a5ce4' 
  AND token = '3f3uoyuFOy4IYXbBcLflbljRhD4MAWMTGC4iKqcj8eA=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00034

JSON explain

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