SELECT 
  SQL_CALC_FOUND_ROWS (
    CASE WHEN products.parent_product_id <> 0 THEN products.parent_product_id ELSE products.product_id END
  ) AS product_id, 
  descr1.product as product, 
  companies.company as company_name, 
  COALESCE(
    cscart_master_products_storefront_min_price.price, 
    MIN(
      IF(
        prices.percentage_discount = 0, 
        prices.price, 
        prices.price - (
          prices.price * prices.percentage_discount
        )/ 100
      )
    )
  ) as price, 
  GROUP_CONCAT(
    products.product_id 
    ORDER BY 
      products.parent_product_id ASC, 
      products.product_id ASC
  ) AS product_ids, 
  GROUP_CONCAT(
    products.product_type 
    ORDER BY 
      products.parent_product_id ASC, 
      products.product_id ASC
  ) AS product_types, 
  GROUP_CONCAT(
    products.parent_product_id 
    ORDER BY 
      products.parent_product_id ASC, 
      products.product_id ASC
  ) AS parent_product_ids, 
  products.product_type, 
  products.parent_product_id, 
  products.master_product_offers_count, 
  products.master_product_id, 
  products.company_id, 
  IF(
    products.age_verification = 'Y', 
    'Y', 
    IF(
      cscart_categories.age_verification = 'Y', 
      'Y', cscart_categories.parent_age_verification
    )
  ) as need_age_verification, 
  IF(
    products.age_limit > cscart_categories.age_limit, 
    IF(
      products.age_limit > cscart_categories.parent_age_limit, 
      products.age_limit, cscart_categories.parent_age_limit
    ), 
    IF(
      cscart_categories.age_limit > cscart_categories.parent_age_limit, 
      cscart_categories.age_limit, cscart_categories.parent_age_limit
    )
  ) as age_limit, 
  1 as instock_marker, 
  IF(
    products.product_type = 'C', 
    (
      SELECT 
        MAX(amount) 
      FROM 
        cscart_products 
      WHERE 
        parent_product_id = products.product_id
    ) > 0, 
    IF(
      IF(
        products.tracking = 'O', 
        (
          SELECT 
            MAX(amount) 
          FROM 
            cscart_product_options_inventory s_inventory 
          WHERE 
            s_inventory.product_id = products.product_id
        ) > 0, 
        products.amount > 0
      ), 
      1, 
      IF(products.tracking = 'D', 1, 0)
    )
  ) as instock_sorting 
FROM 
  cscart_products as products 
  LEFT JOIN cscart_product_descriptions as descr1 ON descr1.product_id = products.product_id 
  AND descr1.lang_code = 'en' 
  LEFT JOIN cscart_product_prices as prices ON prices.product_id = products.product_id 
  AND prices.lower_limit = 1 
  LEFT JOIN cscart_companies AS companies ON companies.company_id = products.company_id 
  INNER JOIN cscart_products_categories as products_categories ON products_categories.product_id = products.product_id 
  INNER JOIN cscart_categories ON cscart_categories.category_id = products_categories.category_id 
  AND (
    cscart_categories.usergroup_ids = '' 
    OR FIND_IN_SET(
      0, cscart_categories.usergroup_ids
    ) 
    OR FIND_IN_SET(
      1, cscart_categories.usergroup_ids
    )
  ) 
  AND cscart_categories.status IN ('A', 'H') 
  AND cscart_categories.storefront_id IN (0, 3) 
  LEFT JOIN cscart_warehouses_sum_products_amount as war_sum_amount ON war_sum_amount.product_id = products.product_id 
  LEFT JOIN cscart_master_products_storefront_offers_count AS master_products_storefront_offers_count ON master_products_storefront_offers_count.product_id = products.product_id 
  AND master_products_storefront_offers_count.storefront_id = 3 
  LEFT JOIN cscart_master_products_storefront_min_price ON cscart_master_products_storefront_min_price.product_id = prices.product_id 
  AND cscart_master_products_storefront_min_price.storefront_id = 3 
WHERE 
  1 
  AND cscart_categories.category_id IN (2300) 
  AND (
    companies.status IN ('A', 'S') 
    OR products.company_id = 0
  ) 
  AND (
    products.usergroup_ids = '' 
    OR FIND_IN_SET(0, products.usergroup_ids) 
    OR FIND_IN_SET(1, products.usergroup_ids)
  ) 
  AND products.status IN ('A') 
  AND prices.usergroup_id IN (0, 0, 1) 
  AND products.master_product_status IN ('A') 
  AND products.master_product_id = 0 
  AND (
    products.company_id > 0 
    OR (
      master_products_storefront_offers_count.count > 0
    )
  ) 
  AND products.product_type != 'D' 
GROUP BY 
  product_id 
ORDER BY 
  instock_sorting DESC, 
  price asc, 
  products.product_id ASC 
LIMIT 
  0, 20

Query time 0.00403

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "18.80"
    },
    "ordering_operation": {
      "using_filesort": true,
      "grouping_operation": {
        "using_temporary_table": true,
        "using_filesort": true,
        "buffer_result": {
          "using_temporary_table": true,
          "nested_loop": [
            {
              "table": {
                "table_name": "war_sum_amount",
                "access_type": "system",
                "possible_keys": [
                  "PRIMARY"
                ],
                "rows_examined_per_scan": 0,
                "rows_produced_per_join": 1,
                "filtered": "0.00",
                "const_row_not_found": true,
                "cost_info": {
                  "read_cost": "0.00",
                  "eval_cost": "0.10",
                  "prefix_cost": "0.00",
                  "data_read_per_join": "16"
                },
                "used_columns": [
                  "product_id"
                ]
              }
            },
            {
              "table": {
                "table_name": "master_products_storefront_offers_count",
                "access_type": "system",
                "possible_keys": [
                  "PRIMARY",
                  "idx_storefront_id"
                ],
                "rows_examined_per_scan": 0,
                "rows_produced_per_join": 1,
                "filtered": "0.00",
                "const_row_not_found": true,
                "cost_info": {
                  "read_cost": "0.00",
                  "eval_cost": "0.10",
                  "prefix_cost": "0.00",
                  "data_read_per_join": "16"
                },
                "used_columns": [
                  "storefront_id",
                  "product_id",
                  "count"
                ]
              }
            },
            {
              "table": {
                "table_name": "cscart_master_products_storefront_min_price",
                "access_type": "system",
                "possible_keys": [
                  "PRIMARY"
                ],
                "rows_examined_per_scan": 0,
                "rows_produced_per_join": 1,
                "filtered": "0.00",
                "const_row_not_found": true,
                "cost_info": {
                  "read_cost": "0.00",
                  "eval_cost": "0.10",
                  "prefix_cost": "0.00",
                  "data_read_per_join": "16"
                },
                "used_columns": [
                  "storefront_id",
                  "product_id",
                  "price"
                ]
              }
            },
            {
              "table": {
                "table_name": "cscart_categories",
                "access_type": "const",
                "possible_keys": [
                  "PRIMARY",
                  "c_status",
                  "p_category_id"
                ],
                "key": "PRIMARY",
                "used_key_parts": [
                  "category_id"
                ],
                "key_length": "3",
                "ref": [
                  "const"
                ],
                "rows_examined_per_scan": 1,
                "rows_produced_per_join": 1,
                "filtered": "100.00",
                "cost_info": {
                  "read_cost": "0.00",
                  "eval_cost": "0.10",
                  "prefix_cost": "0.00",
                  "data_read_per_join": "3K"
                },
                "used_columns": [
                  "category_id",
                  "usergroup_ids",
                  "status",
                  "age_verification",
                  "age_limit",
                  "parent_age_verification",
                  "parent_age_limit",
                  "storefront_id"
                ]
              }
            },
            {
              "table": {
                "table_name": "products_categories",
                "access_type": "ref",
                "possible_keys": [
                  "PRIMARY",
                  "pt"
                ],
                "key": "PRIMARY",
                "used_key_parts": [
                  "category_id"
                ],
                "key_length": "3",
                "ref": [
                  "const"
                ],
                "rows_examined_per_scan": 73,
                "rows_produced_per_join": 73,
                "filtered": "100.00",
                "using_index": true,
                "cost_info": {
                  "read_cost": "0.70",
                  "eval_cost": "7.30",
                  "prefix_cost": "8.00",
                  "data_read_per_join": "1K"
                },
                "used_columns": [
                  "product_id",
                  "category_id"
                ]
              }
            },
            {
              "table": {
                "table_name": "products",
                "access_type": "eq_ref",
                "possible_keys": [
                  "PRIMARY",
                  "status",
                  "idx_master_product_id"
                ],
                "key": "PRIMARY",
                "used_key_parts": [
                  "product_id"
                ],
                "key_length": "3",
                "ref": [
                  "s2cart.products_categories.product_id"
                ],
                "rows_examined_per_scan": 1,
                "rows_produced_per_join": 6,
                "filtered": "8.72",
                "cost_info": {
                  "read_cost": "0.00",
                  "eval_cost": "0.64",
                  "prefix_cost": "15.30",
                  "data_read_per_join": "48K"
                },
                "used_columns": [
                  "product_id",
                  "product_type",
                  "status",
                  "company_id",
                  "amount",
                  "usergroup_ids",
                  "tracking",
                  "age_verification",
                  "age_limit",
                  "parent_product_id",
                  "master_product_id",
                  "master_product_status",
                  "master_product_offers_count"
                ],
                "attached_condition": "((`s2cart`.`products`.`master_product_id` = 0) and ((`s2cart`.`products`.`usergroup_ids` = '') or (0 <> find_in_set(0,`s2cart`.`products`.`usergroup_ids`)) or (0 <> find_in_set(1,`s2cart`.`products`.`usergroup_ids`))) and (`s2cart`.`products`.`status` = 'A') and (`s2cart`.`products`.`master_product_status` = 'A') and ((`s2cart`.`products`.`company_id` > 0) or <cache>((NULL > 0))) and (`s2cart`.`products`.`product_type` <> 'D'))"
              }
            },
            {
              "table": {
                "table_name": "companies",
                "access_type": "eq_ref",
                "possible_keys": [
                  "PRIMARY"
                ],
                "key": "PRIMARY",
                "used_key_parts": [
                  "company_id"
                ],
                "key_length": "4",
                "ref": [
                  "s2cart.products.company_id"
                ],
                "rows_examined_per_scan": 1,
                "rows_produced_per_join": 6,
                "filtered": "100.00",
                "cost_info": {
                  "read_cost": "0.00",
                  "eval_cost": "0.64",
                  "prefix_cost": "15.94",
                  "data_read_per_join": "59K"
                },
                "used_columns": [
                  "company_id",
                  "status",
                  "company"
                ],
                "attached_condition": "<if>(found_match(companies), ((`s2cart`.`companies`.`status` in ('A','S')) or (`s2cart`.`products`.`company_id` = 0)), true)"
              }
            },
            {
              "table": {
                "table_name": "descr1",
                "access_type": "eq_ref",
                "possible_keys": [
                  "PRIMARY",
                  "product_id"
                ],
                "key": "PRIMARY",
                "used_key_parts": [
                  "product_id",
                  "lang_code"
                ],
                "key_length": "9",
                "ref": [
                  "s2cart.products_categories.product_id",
                  "const"
                ],
                "rows_examined_per_scan": 1,
                "rows_produced_per_join": 6,
                "filtered": "100.00",
                "cost_info": {
                  "read_cost": "0.00",
                  "eval_cost": "0.64",
                  "prefix_cost": "16.57",
                  "data_read_per_join": "48K"
                },
                "used_columns": [
                  "product_id",
                  "lang_code",
                  "product"
                ]
              }
            },
            {
              "table": {
                "table_name": "prices",
                "access_type": "ref",
                "possible_keys": [
                  "usergroup",
                  "product_id",
                  "lower_limit",
                  "usergroup_id"
                ],
                "key": "product_id",
                "used_key_parts": [
                  "product_id"
                ],
                "key_length": "3",
                "ref": [
                  "s2cart.products_categories.product_id"
                ],
                "rows_examined_per_scan": 1,
                "rows_produced_per_join": 6,
                "filtered": "100.00",
                "cost_info": {
                  "read_cost": "1.59",
                  "eval_cost": "0.64",
                  "prefix_cost": "18.80",
                  "data_read_per_join": "152"
                },
                "used_columns": [
                  "product_id",
                  "price",
                  "percentage_discount",
                  "lower_limit",
                  "usergroup_id"
                ],
                "attached_condition": "((`s2cart`.`prices`.`lower_limit` = 1) and (`s2cart`.`prices`.`usergroup_id` in (0,0,1)))"
              }
            }
          ],
          "select_list_subqueries": [
            {
              "dependent": true,
              "cacheable": false,
              "query_block": {
                "select_id": 3,
                "message": "no matching row in const table"
              }
            },
            {
              "dependent": true,
              "cacheable": false,
              "query_block": {
                "select_id": 2,
                "cost_info": {
                  "query_cost": "31651.29"
                },
                "table": {
                  "table_name": "cscart_products",
                  "access_type": "ALL",
                  "possible_keys": [
                    "idx_parent_product_id"
                  ],
                  "rows_examined_per_scan": 270845,
                  "rows_produced_per_join": 27084,
                  "filtered": "10.00",
                  "cost_info": {
                    "read_cost": "4566.79",
                    "eval_cost": "2708.45",
                    "prefix_cost": "31651.29",
                    "data_read_per_join": "203M"
                  },
                  "used_columns": [
                    "amount",
                    "parent_product_id"
                  ],
                  "attached_condition": "(`s2cart`.`cscart_products`.`parent_product_id` = `s2cart`.`products`.`product_id`)"
                }
              }
            }
          ]
        }
      }
    }
  }
}