SELECT 
  `cscart_products`.`product_id` 
FROM 
  `cscart_products` 
  LEFT JOIN `cscart_products_categories` ON `cscart_products`.`product_id` = `cscart_products_categories`.`product_id` 
WHERE 
  `cscart_products`.`company_id` = 687 
  AND `cscart_products`.`status` = 'A' 
  AND `cscart_products_categories`.`category_id` = 603

Query time 0.00046

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "16.95"
    },
    "nested_loop": [
      {
        "table": {
          "table_name": "cscart_products_categories",
          "access_type": "ref",
          "possible_keys": [
            "PRIMARY",
            "pt",
            "idx_pc_product_id_type"
          ],
          "key": "PRIMARY",
          "used_key_parts": [
            "category_id"
          ],
          "key_length": "3",
          "ref": [
            "const"
          ],
          "rows_examined_per_scan": 37,
          "rows_produced_per_join": 37,
          "filtered": "100.00",
          "using_index": true,
          "cost_info": {
            "read_cost": "0.30",
            "eval_cost": "3.70",
            "prefix_cost": "4.00",
            "data_read_per_join": "592"
          },
          "used_columns": [
            "product_id",
            "category_id"
          ],
          "attached_condition": "(`dev2`.`cscart_products_categories`.`product_id` is not null)"
        }
      },
      {
        "table": {
          "table_name": "cscart_products",
          "access_type": "eq_ref",
          "possible_keys": [
            "PRIMARY",
            "status",
            "cscart_products_product_id_index",
            "idx_status"
          ],
          "key": "PRIMARY",
          "used_key_parts": [
            "product_id"
          ],
          "key_length": "3",
          "ref": [
            "dev2.cscart_products_categories.product_id"
          ],
          "rows_examined_per_scan": 1,
          "rows_produced_per_join": 2,
          "filtered": "7.22",
          "cost_info": {
            "read_cost": "9.25",
            "eval_cost": "0.27",
            "prefix_cost": "16.95",
            "data_read_per_join": "20K"
          },
          "used_columns": [
            "product_id",
            "status",
            "company_id"
          ],
          "attached_condition": "((`dev2`.`cscart_products`.`company_id` = 687) and (`dev2`.`cscart_products`.`status` = 'A'))"
        }
      }
    ]
  }
}