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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '50c7ef62ce694aeb7275428a6ecba3d3a9cb6814c9b157602652b7343fa866b2' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00015

JSON explain

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