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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '51a1151e8e99d83b94af89694c6816d514e09453e21148c6ef26ab0b84a6e0d2' 
  AND token = 'dTimoax7FKRwjBv6X7tFVP29VNrP1D//QMO1fzGVbmM=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00028

JSON explain

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