SELECT 
  SQL_CALC_FOUND_ROWS products.product_id, 
  IF(
    shared_descr.product_id IS NOT NULL, 
    shared_descr.product, descr1.product
  ) as product, 
  products.product_type, 
  products.parent_product_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 
FROM 
  cscart_products as products 
  LEFT JOIN cscart_product_descriptions as descr1 ON descr1.product_id = products.product_id 
  AND descr1.lang_code = 'ru' 
  LEFT JOIN cscart_product_prices as prices ON prices.product_id = products.product_id 
  AND prices.lower_limit = 1 
  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') 
  LEFT JOIN cscart_ult_product_descriptions shared_descr ON shared_descr.product_id = products.product_id 
  AND shared_descr.company_id = 1 
  AND shared_descr.lang_code = 'ru' 
  LEFT JOIN cscart_product_options_inventory as inventory_b ON inventory_b.product_id = products.product_id 
  AND inventory_b.amount >= 1 
WHERE 
  1 
  AND cscart_categories.category_id IN (1, 2, 3, 4, 5, 6, 7) 
  AND products.product_id NOT IN (5) 
  AND cscart_categories.company_id = 1 
  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.parent_product_id = 0 
  AND (
    IF(
      products.tracking = 'O', inventory_b.amount >= 1, 
      products.amount >= 1
    ) 
    OR (products.tracking = 'D')
  ) 
GROUP BY 
  products.product_id 
ORDER BY 
  product desc, 
  products.product_id ASC 
LIMIT 
  0, 4

Query time 0.00245

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "6.28"
    },
    "ordering_operation": {
      "using_filesort": true,
      "grouping_operation": {
        "using_temporary_table": true,
        "using_filesort": false,
        "nested_loop": [
          {
            "table": {
              "table_name": "shared_descr",
              "access_type": "system",
              "possible_keys": [
                "PRIMARY",
                "product_id",
                "company_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": "0.20",
                "prefix_cost": "0.00",
                "data_read_per_join": "3K"
              },
              "used_columns": [
                "product_id",
                "lang_code",
                "company_id",
                "product"
              ]
            }
          },
          {
            "table": {
              "table_name": "inventory_b",
              "access_type": "system",
              "possible_keys": [
                "pc"
              ],
              "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": "0.20",
                "prefix_cost": "0.00",
                "data_read_per_join": "976"
              },
              "used_columns": [
                "product_id",
                "amount"
              ]
            }
          },
          {
            "table": {
              "table_name": "prices",
              "access_type": "ref",
              "possible_keys": [
                "usergroup",
                "product_id",
                "lower_limit",
                "usergroup_id"
              ],
              "key": "lower_limit",
              "used_key_parts": [
                "lower_limit"
              ],
              "key_length": "3",
              "ref": [
                "const"
              ],
              "rows_examined_per_scan": 5,
              "rows_produced_per_join": 2,
              "filtered": "50.00",
              "cost_info": {
                "read_cost": "2.00",
                "eval_cost": "0.50",
                "prefix_cost": "3.00",
                "data_read_per_join": "60"
              },
              "used_columns": [
                "product_id",
                "lower_limit",
                "usergroup_id"
              ],
              "attached_condition": "(((`db_emaika1`.`prices`.`product_id` <> 5) and (`db_emaika1`.`prices`.`usergroup_id` in (0,0,1))) and ((`db_emaika1`.`prices`.`product_id` is not null) and (`db_emaika1`.`prices`.`product_id` is not null)))"
            }
          },
          {
            "table": {
              "table_name": "products",
              "access_type": "eq_ref",
              "possible_keys": [
                "PRIMARY",
                "status",
                "idx_parent_product_id"
              ],
              "key": "PRIMARY",
              "used_key_parts": [
                "product_id"
              ],
              "key_length": "3",
              "ref": [
                "db_emaika1.prices.product_id"
              ],
              "rows_examined_per_scan": 1,
              "rows_produced_per_join": 1,
              "filtered": "69.44",
              "cost_info": {
                "read_cost": "0.00",
                "eval_cost": "0.35",
                "prefix_cost": "3.50",
                "data_read_per_join": "13K"
              },
              "used_columns": [
                "product_id",
                "product_type",
                "status",
                "amount",
                "usergroup_ids",
                "tracking",
                "age_verification",
                "age_limit",
                "parent_product_id"
              ],
              "attached_condition": "((`db_emaika1`.`products`.`parent_product_id` = 0) and ((`db_emaika1`.`products`.`usergroup_ids` = '') or find_in_set(0,`db_emaika1`.`products`.`usergroup_ids`) or find_in_set(1,`db_emaika1`.`products`.`usergroup_ids`)) and (`db_emaika1`.`products`.`status` = 'A') and (if((`db_emaika1`.`products`.`tracking` = 'O'),<cache>((NULL >= 1)),(`db_emaika1`.`products`.`amount` >= 1)) or (`db_emaika1`.`products`.`tracking` = 'D')))"
            }
          },
          {
            "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": [
                "db_emaika1.prices.product_id",
                "const"
              ],
              "rows_examined_per_scan": 1,
              "rows_produced_per_join": 1,
              "filtered": "100.00",
              "cost_info": {
                "read_cost": "0.00",
                "eval_cost": "0.35",
                "prefix_cost": "3.85",
                "data_read_per_join": "6K"
              },
              "used_columns": [
                "product_id",
                "lang_code",
                "product"
              ]
            }
          },
          {
            "table": {
              "table_name": "products_categories",
              "access_type": "ref",
              "possible_keys": [
                "PRIMARY",
                "pt"
              ],
              "key": "pt",
              "used_key_parts": [
                "product_id"
              ],
              "key_length": "3",
              "ref": [
                "db_emaika1.prices.product_id"
              ],
              "rows_examined_per_scan": 1,
              "rows_produced_per_join": 1,
              "filtered": "100.00",
              "cost_info": {
                "read_cost": "1.74",
                "eval_cost": "0.35",
                "prefix_cost": "5.93",
                "data_read_per_join": "27"
              },
              "used_columns": [
                "product_id",
                "category_id"
              ],
              "attached_condition": "(`db_emaika1`.`products_categories`.`category_id` in (1,2,3,4,5,6,7))"
            }
          },
          {
            "table": {
              "table_name": "cscart_categories",
              "access_type": "eq_ref",
              "possible_keys": [
                "PRIMARY",
                "c_status",
                "p_category_id"
              ],
              "key": "PRIMARY",
              "used_key_parts": [
                "category_id"
              ],
              "key_length": "3",
              "ref": [
                "db_emaika1.products_categories.category_id"
              ],
              "rows_examined_per_scan": 1,
              "rows_produced_per_join": 0,
              "filtered": "14.29",
              "cost_info": {
                "read_cost": "0.00",
                "eval_cost": "0.05",
                "prefix_cost": "6.28",
                "data_read_per_join": "1017"
              },
              "used_columns": [
                "category_id",
                "company_id",
                "usergroup_ids",
                "status",
                "age_verification",
                "age_limit",
                "parent_age_verification",
                "parent_age_limit"
              ],
              "attached_condition": "((`db_emaika1`.`cscart_categories`.`company_id` = 1) and ((`db_emaika1`.`cscart_categories`.`usergroup_ids` = '') or find_in_set(0,`db_emaika1`.`cscart_categories`.`usergroup_ids`) or find_in_set(1,`db_emaika1`.`cscart_categories`.`usergroup_ids`)) and (`db_emaika1`.`cscart_categories`.`status` in ('A','H')))"
            }
          }
        ]
      }
    }
  }
}