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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '5402895c37ca17262b7d690ca7fcfca6d30986391b5f5a505c81a6185013eb1f' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00026

JSON explain

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