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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'a621d2027fa4a3e496716f7e81eeccec38831be0ccc33a2d346363a2a1667ef0' 
  AND token = 'pVTwJSmemFOJMhtNqTsqsiMkPA9bfTqjcUFT4Y/vSbk=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00028

JSON explain

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