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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '83689d35f6e7f08efcde334779d717a278a1891ad5c6a8da1076008a14b934c0' 
  AND token = '6wtz3JkMdRlnJKIyPr3IsGNOHs4WkhdEdYLzMJa+OxQ=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00016

JSON explain

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