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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '559232f6abad2af5a1f0071224ae1f646b9a3696b33fb7e377dd787ead5db0d6' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00019

JSON explain

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