SELECT 
  cscart_product_sales.product_id, 
  amount AS sales_amount 
FROM 
  cscart_product_sales 
  LEFT JOIN cscart_products_categories ON cscart_products_categories.product_id = cscart_product_sales.product_id 
  AND cscart_products_categories.category_id = cscart_product_sales.category_id 
WHERE 
  cscart_product_sales.product_id IN (504, 1817) 
  AND cscart_products_categories.link_type = 'M'

Query time 0.00051

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "cscart_product_sales",
      "access_type": "range",
      "possible_keys": ["PRIMARY", "pa"],
      "key": "pa",
      "key_length": "3",
      "used_key_parts": ["product_id"],
      "rows": 2,
      "filtered": 100,
      "index_condition": "cscart_product_sales.product_id in (504,1817)"
    },
    "table": {
      "table_name": "cscart_products_categories",
      "access_type": "eq_ref",
      "possible_keys": ["PRIMARY", "link_type", "pt"],
      "key": "PRIMARY",
      "key_length": "6",
      "used_key_parts": ["category_id", "product_id"],
      "ref": [
        "bacpvdev_db.cscart_product_sales.category_id",
        "bacpvdev_db.cscart_product_sales.product_id"
      ],
      "rows": 1,
      "filtered": 100,
      "attached_condition": "cscart_products_categories.link_type = 'M'"
    }
  }
}