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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '8420aac01ae7be36173791b90df843498f9cd19f6063782a888b4ad0c1091850' 
  AND token = 'zMgN4dNAaMrVEFhxlQa9yfbuovf6KInoFhPGhy1BjMw=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00021

JSON explain

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