Sandbox

SELECT 
  req_prod.required_id 
FROM 
  cscart_product_required_products as req_prod 
  LEFT JOIN cscart_products ON req_prod.required_id = cscart_products.product_id 
WHERE 
  req_prod.product_id = 661 
  AND cscart_products.status != 'D' 
GROUP BY 
  req_prod.required_id

Query time 0.00010

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "message": "Impossible WHERE noticed after reading const tables"
    }
  }
}