SELECT 
  SUM(products.amount) 
FROM 
  cscart_products AS products 
  INNER JOIN cscart_companies AS company ON products.company_id = company.company_id 
WHERE 
  products.master_product_id = 806 
  AND products.status IN ('A') 
  AND company.status IN ('A') 
  AND company.company_id IN (
    2, 3, 4, 7, 14, 15, 21, 23, 25, 26, 27, 28, 
    30, 31, 33, 34, 35, 36, 37, 38, 40, 72, 
    73, 74, 78, 89
  )

Query time 0.00031

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost": 0.007301091,
    "nested_loop": [
      {
        "table": {
          "table_name": "products",
          "access_type": "ref",
          "possible_keys": ["status", "idx_master_product_id"],
          "key": "idx_master_product_id",
          "key_length": "4",
          "used_key_parts": ["master_product_id"],
          "ref": ["const"],
          "loops": 1,
          "rows": 2,
          "cost": 0.0052712,
          "filtered": 59.22746658,
          "attached_condition": "products.`status` = 'A'"
        }
      },
      {
        "table": {
          "table_name": "company",
          "access_type": "eq_ref",
          "possible_keys": ["PRIMARY"],
          "key": "PRIMARY",
          "key_length": "4",
          "used_key_parts": ["company_id"],
          "ref": ["u428615623_ecartifygonje.products.company_id"],
          "loops": 1.184549356,
          "rows": 1,
          "cost": 0.002029891,
          "filtered": 100,
          "attached_condition": "company.`status` = 'A' and company.company_id in (2,3,4,7,14,15,21,23,25,26,27,28,30,31,33,34,35,36,37,38,40,72,73,74,78,89)"
        }
      }
    ]
  }
}