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, 
  IF(
    shared_descr.product_id IS NOT NULL, 
    shared_descr.product, descr1.product
  ) as product, 
  IF(
    shared_prices.product_id IS NOT NULL, 
    MIN(
      IF (
        shared_prices.percentage_discount = 0, 
        shared_prices.price, 
        shared_prices.price - (
          shared_prices.price * shared_prices.percentage_discount
        ) / 100
      )
    ), 
    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, 
  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 
  LEFT JOIN cscart_product_prices as prices_2 ON prices.product_id = prices_2.product_id 
  AND prices_2.lower_limit = 1 
  AND prices_2.price < prices.price 
  AND prices_2.usergroup_id IN (0, 0, 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_ult_product_prices as shared_prices ON shared_prices.product_id = products.product_id 
  AND shared_prices.lower_limit = 1 
  AND shared_prices.usergroup_id IN (0, 0, 1) 
  AND shared_prices.company_id = 1 
  LEFT JOIN cscart_ult_product_prices as shared_prices_2 ON shared_prices.product_id = shared_prices_2.product_id 
  AND shared_prices_2.company_id = 1 
  AND shared_prices_2.lower_limit = 1 
  AND shared_prices_2.price < shared_prices.price 
  AND shared_prices_2.usergroup_id IN (0, 0, 1) 
WHERE 
  1 
  AND products.product_id NOT IN (4) 
  AND cscart_categories.company_id = 1 
  AND (
    prices.price >= 0.00 
    OR shared_prices.price >= 0.00
  ) 
  AND (
    prices.price <= 0.00 
    OR shared_prices.price <= 0.00
  ) 
  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 prices_2.price IS NULL 
  AND shared_prices_2.price IS NULL 
GROUP BY 
  product_id 
ORDER BY 
  product desc, 
  products.product_id ASC 
LIMIT 
  0, 3

Query time 0.00309

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "7.63"
    },
    "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": "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": "shared_prices",
                "access_type": "system",
                "possible_keys": [
                  "usergroup",
                  "product_id",
                  "company_id",
                  "lower_limit",
                  "usergroup_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": "32"
                },
                "used_columns": [
                  "product_id",
                  "price",
                  "percentage_discount",
                  "lower_limit",
                  "company_id",
                  "usergroup_id"
                ]
              }
            },
            {
              "table": {
                "table_name": "shared_prices_2",
                "access_type": "system",
                "possible_keys": [
                  "usergroup",
                  "product_id",
                  "company_id",
                  "lower_limit",
                  "usergroup_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": "32"
                },
                "used_columns": [
                  "product_id",
                  "price",
                  "lower_limit",
                  "company_id",
                  "usergroup_id"
                ]
              }
            },
            {
              "table": {
                "table_name": "products_categories",
                "access_type": "index",
                "possible_keys": [
                  "PRIMARY",
                  "pt"
                ],
                "key": "PRIMARY",
                "used_key_parts": [
                  "category_id",
                  "product_id"
                ],
                "key_length": "6",
                "rows_examined_per_scan": 6,
                "rows_produced_per_join": 6,
                "filtered": "100.00",
                "using_index": true,
                "cost_info": {
                  "read_cost": "2.02",
                  "eval_cost": "1.20",
                  "prefix_cost": "3.22",
                  "data_read_per_join": "96"
                },
                "used_columns": [
                  "product_id",
                  "category_id"
                ],
                "attached_condition": "(`db_emaika1`.`products_categories`.`product_id` <> 4)"
              }
            },
            {
              "table": {
                "table_name": "products",
                "access_type": "eq_ref",
                "possible_keys": [
                  "PRIMARY",
                  "status"
                ],
                "key": "PRIMARY",
                "used_key_parts": [
                  "product_id"
                ],
                "key_length": "3",
                "ref": [
                  "db_emaika1.products_categories.product_id"
                ],
                "rows_examined_per_scan": 1,
                "rows_produced_per_join": 4,
                "filtered": "83.33",
                "cost_info": {
                  "read_cost": "0.00",
                  "eval_cost": "1.00",
                  "prefix_cost": "4.42",
                  "data_read_per_join": "39K"
                },
                "used_columns": [
                  "product_id",
                  "product_type",
                  "status",
                  "usergroup_ids",
                  "age_verification",
                  "age_limit",
                  "parent_product_id"
                ],
                "attached_condition": "(((`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'))"
              }
            },
            {
              "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.products_categories.product_id",
                  "const"
                ],
                "rows_examined_per_scan": 1,
                "rows_produced_per_join": 4,
                "filtered": "100.00",
                "cost_info": {
                  "read_cost": "0.00",
                  "eval_cost": "1.00",
                  "prefix_cost": "5.42",
                  "data_read_per_join": "19K"
                },
                "used_columns": [
                  "product_id",
                  "lang_code",
                  "product"
                ]
              }
            },
            {
              "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": "0.14",
                  "prefix_cost": "6.42",
                  "data_read_per_join": "2K"
                },
                "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')))"
              }
            },
            {
              "table": {
                "table_name": "prices",
                "access_type": "ref",
                "possible_keys": [
                  "usergroup",
                  "product_id",
                  "lower_limit",
                  "usergroup_id"
                ],
                "key": "usergroup",
                "used_key_parts": [
                  "product_id"
                ],
                "key_length": "3",
                "ref": [
                  "db_emaika1.products_categories.product_id"
                ],
                "rows_examined_per_scan": 1,
                "rows_produced_per_join": 0,
                "filtered": "41.67",
                "index_condition": "((`db_emaika1`.`prices`.`lower_limit` = 1) and (`db_emaika1`.`prices`.`usergroup_id` in (0,0,1)))",
                "cost_info": {
                  "read_cost": "0.71",
                  "eval_cost": "0.06",
                  "prefix_cost": "7.28",
                  "data_read_per_join": "7"
                },
                "used_columns": [
                  "product_id",
                  "price",
                  "percentage_discount",
                  "lower_limit",
                  "usergroup_id"
                ],
                "attached_condition": "(((`db_emaika1`.`prices`.`price` >= 0.00) or <cache>((NULL >= 0.00))) and ((`db_emaika1`.`prices`.`price` <= 0.00) or <cache>((NULL <= 0.00))))"
              }
            },
            {
              "table": {
                "table_name": "prices_2",
                "access_type": "ref",
                "possible_keys": [
                  "usergroup",
                  "product_id",
                  "lower_limit",
                  "usergroup_id"
                ],
                "key": "usergroup",
                "used_key_parts": [
                  "product_id"
                ],
                "key_length": "3",
                "ref": [
                  "db_emaika1.products_categories.product_id"
                ],
                "rows_examined_per_scan": 1,
                "rows_produced_per_join": 0,
                "filtered": "16.67",
                "not_exists": true,
                "cost_info": {
                  "read_cost": "0.30",
                  "eval_cost": "0.01",
                  "prefix_cost": "7.63",
                  "data_read_per_join": "1"
                },
                "used_columns": [
                  "product_id",
                  "price",
                  "lower_limit",
                  "usergroup_id"
                ],
                "attached_condition": "(<if>(found_match(prices_2), isnull(`db_emaika1`.`prices_2`.`price`), true) and <if>(is_not_null_compl(prices_2), ((`db_emaika1`.`prices_2`.`lower_limit` = 1) and (`db_emaika1`.`prices_2`.`price` < `db_emaika1`.`prices`.`price`) and (`db_emaika1`.`prices_2`.`usergroup_id` in (0,0,1))), true))"
              }
            }
          ]
        }
      }
    }
  }
}