SELECT 
  product_id 
FROM 
  cscart_products 
WHERE 
  product_type = 'D'

Query time 0.10748

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost": 113.2641975,
    "nested_loop": [
      {
        "table": {
          "table_name": "cscart_products",
          "access_type": "index",
          "key": "wdbi_master_product_id_master_product_status_produc_611007cab252",
          "key_length": "10",
          "used_key_parts": [
            "master_product_id",
            "master_product_status",
            "product_type"
          ],
          "loops": 1,
          "rows": 767388,
          "cost": 113.2641975,
          "filtered": 100,
          "attached_condition": "cscart_products.product_type = 'D'",
          "using_index": true
        }
      }
    ]
  }
}