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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '5cd7e9f0a8e09a6cf962413ea58695c37295f2a500c5e8c8c081be2bec253d36' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00034

JSON explain

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