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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'b20dbdf2bcd18332a0ee9a646783d3b079ed4f5fa9f8f7c80cb802278e63dc1b' 
  AND token = 'THMSdwFXgcAa3+4Q3Zd9JGOdArUWNjNBtt1iDnO6Fi0=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00018

JSON explain

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