SELECT 
  COUNT(
    DISTINCT(cscart_pages.page_id)
  ) 
FROM 
  cscart_pages 
  LEFT JOIN cscart_page_descriptions ON cscart_pages.page_id = cscart_page_descriptions.page_id 
  AND cscart_page_descriptions.lang_code = 'ru' 
  LEFT JOIN cscart_seo_names ON cscart_seo_names.object_id = cscart_pages.page_id 
  AND cscart_seo_names.type = 'a' 
  AND cscart_seo_names.dispatch = '' 
  AND cscart_seo_names.lang_code = 'ru' 
  INNER JOIN cscart_ult_objects_sharing ON (
    cscart_ult_objects_sharing.share_object_id = cscart_pages.page_id 
    AND cscart_ult_objects_sharing.share_company_id = 1 
    AND cscart_ult_objects_sharing.share_object_type = 'pages'
  ) 
WHERE 
  1 
  AND cscart_pages.parent_id IN (7) 
  AND cscart_pages.status IN ('A') 
  AND cscart_pages.page_type IN ('B') 
  AND (
    cscart_pages.usergroup_ids = '' 
    OR FIND_IN_SET(0, cscart_pages.usergroup_ids) 
    OR FIND_IN_SET(1, cscart_pages.usergroup_ids)
  ) 
  AND (
    cscart_pages.use_avail_period = 'N' 
    OR (
      cscart_pages.use_avail_period = 'Y' 
      AND cscart_pages.avail_from_timestamp <= 1774755576 
      AND (
        cscart_pages.avail_till_timestamp >= 1774755576 
        OR cscart_pages.avail_till_timestamp = 0
      )
    )
  ) 
ORDER BY 
  cscart_pages.timestamp desc

Query time 0.00103

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "2.24"
    },
    "nested_loop": [
      {
        "table": {
          "table_name": "cscart_pages",
          "access_type": "ref",
          "possible_keys": [
            "PRIMARY",
            "parent_id"
          ],
          "key": "parent_id",
          "used_key_parts": [
            "parent_id"
          ],
          "key_length": "3",
          "ref": [
            "const"
          ],
          "rows_examined_per_scan": 9,
          "rows_produced_per_join": 0,
          "filtered": "4.35",
          "cost_info": {
            "read_cost": "0.57",
            "eval_cost": "0.04",
            "prefix_cost": "1.48",
            "data_read_per_join": "1K"
          },
          "used_columns": [
            "page_id",
            "parent_id",
            "status",
            "page_type",
            "timestamp",
            "usergroup_ids",
            "use_avail_period",
            "avail_from_timestamp",
            "avail_till_timestamp"
          ],
          "attached_condition": "((`zdrowy_db`.`cscart_pages`.`status` = 'A') and (`zdrowy_db`.`cscart_pages`.`page_type` = 'B') and ((`zdrowy_db`.`cscart_pages`.`usergroup_ids` = '') or (0 <> find_in_set(0,`zdrowy_db`.`cscart_pages`.`usergroup_ids`)) or (0 <> find_in_set(1,`zdrowy_db`.`cscart_pages`.`usergroup_ids`))) and ((`zdrowy_db`.`cscart_pages`.`use_avail_period` = 'N') or ((`zdrowy_db`.`cscart_pages`.`use_avail_period` = 'Y') and (`zdrowy_db`.`cscart_pages`.`avail_from_timestamp` <= 1774755576) and ((`zdrowy_db`.`cscart_pages`.`avail_till_timestamp` >= 1774755576) or (`zdrowy_db`.`cscart_pages`.`avail_till_timestamp` = 0)))))"
        }
      },
      {
        "table": {
          "table_name": "cscart_page_descriptions",
          "access_type": "eq_ref",
          "possible_keys": [
            "PRIMARY"
          ],
          "key": "PRIMARY",
          "used_key_parts": [
            "page_id",
            "lang_code"
          ],
          "key_length": "9",
          "ref": [
            "zdrowy_db.cscart_pages.page_id",
            "const"
          ],
          "rows_examined_per_scan": 1,
          "rows_produced_per_join": 0,
          "filtered": "100.00",
          "using_index": true,
          "cost_info": {
            "read_cost": "0.10",
            "eval_cost": "0.04",
            "prefix_cost": "1.61",
            "data_read_per_join": "1K"
          },
          "used_columns": [
            "page_id",
            "lang_code"
          ]
        }
      },
      {
        "table": {
          "table_name": "cscart_ult_objects_sharing",
          "access_type": "eq_ref",
          "possible_keys": [
            "PRIMARY"
          ],
          "key": "PRIMARY",
          "used_key_parts": [
            "share_object_id",
            "share_company_id",
            "share_object_type"
          ],
          "key_length": "159",
          "ref": [
            "zdrowy_db.cscart_pages.page_id",
            "const",
            "const"
          ],
          "rows_examined_per_scan": 1,
          "rows_produced_per_join": 0,
          "filtered": "100.00",
          "using_index": true,
          "cost_info": {
            "read_cost": "0.10",
            "eval_cost": "0.04",
            "prefix_cost": "1.75",
            "data_read_per_join": "62"
          },
          "used_columns": [
            "share_company_id",
            "share_object_id",
            "share_object_type"
          ],
          "attached_condition": "(`zdrowy_db`.`cscart_ult_objects_sharing`.`share_object_id` = `zdrowy_db`.`cscart_pages`.`page_id`)"
        }
      },
      {
        "table": {
          "table_name": "cscart_seo_names",
          "access_type": "ref",
          "possible_keys": [
            "PRIMARY",
            "dispatch"
          ],
          "key": "PRIMARY",
          "used_key_parts": [
            "object_id",
            "type",
            "dispatch",
            "lang_code"
          ],
          "key_length": "206",
          "ref": [
            "zdrowy_db.cscart_pages.page_id",
            "const",
            "const",
            "const"
          ],
          "rows_examined_per_scan": 6,
          "rows_produced_per_join": 2,
          "filtered": "100.00",
          "using_index": true,
          "cost_info": {
            "read_cost": "0.26",
            "eval_cost": "0.23",
            "prefix_cost": "2.24",
            "data_read_per_join": "3K"
          },
          "used_columns": [
            "object_id",
            "type",
            "dispatch",
            "lang_code"
          ]
        }
      }
    ]
  }
}