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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '911c99cb25de09a7488871d86163aa6532805e00b30d3b7f5b8b91cd0f3d5f81' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00016

JSON explain

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