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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'b3c79ba1986b31cd12cdc35509efec2d39750f2d138b31246bb6b3ed564a94ca' 
  AND token = 'j68JJen1R9ZCz3h+9ZPzqPRgtWTJExcT5AR0nrb8owk=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00018

JSON explain

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