Merge pull request #27536 from adevyatova/annadevyatova-DOCSUP-11968-explain

DOCSUP-11968: Document the SQL-statement EXPLAIN ESTIMATE

docs/en/engines/database-engines/replicated.md

@@ -1,3 +1,8 @@
+---
+toc_priority: 36
+toc_title: Replicated
+---
+
 # [experimental] Replicated {#replicated}
 
 The engine is based on the [Atomic](../../engines/database-engines/atomic.md) engine. It supports replication of metadata via DDL log being written to ZooKeeper and executed on all of the replicas for a given database.

docs/en/sql-reference/statements/explain.md

@@ -384,5 +384,32 @@ ExpressionTransform
             (ReadFromStorage)
             NumbersMt × 2 0 → 1
 ```
+### EXPLAIN ESTIMATE {#explain-estimate}
+
+Shows the estimated number of rows, marks and parts to be read from the tables while processing the query. Works with tables in the [MergeTree](../../engines/table-engines/mergetree-family/mergetree.md#table_engines-mergetree) family. 
+
+**Example**
+
+Creating a table:
+
+```sql
+CREATE TABLE ttt (i Int64) ENGINE = MergeTree() ORDER BY i SETTINGS index_granularity = 16, write_final_mark = 0;
+INSERT INTO ttt SELECT number FROM numbers(128);
+OPTIMIZE TABLE ttt;
+```
+
+Query:
+
+```sql
+EXPLAIN ESTIMATE SELECT * FROM ttt;
+```
+
+Result:
+
+```text
+┌─database─┬─table─┬─parts─┬─rows─┬─marks─┐
+│ default  │ ttt   │     1 │  128 │     8 │
+└──────────┴───────┴───────┴──────┴───────┘
+```
 
 [Оriginal article](https://clickhouse.tech/docs/en/sql-reference/statements/explain/) <!--hide-->

docs/ru/engines/database-engines/replicated.md

@@ -1,3 +1,7 @@
+---
+toc_priority: 36
+toc_title: Replicated
+---
 
 # [экспериментальный] Replicated {#replicated}
 

docs/ru/sql-reference/statements/explain.md

@@ -385,4 +385,32 @@ ExpressionTransform
             NumbersMt × 2 0 → 1
 ```
 
+### EXPLAIN ESTIMATE {#explain-estimate}
+
+ Отображает оценки числа строк, засечек и кусков, которые будут прочитаны при выполнении запроса. Применяется для таблиц семейства [MergeTree](../../engines/table-engines/mergetree-family/mergetree.md#table_engines-mergetree). 
+
+**Пример**
+
+Создадим таблицу:
+
+```sql
+CREATE TABLE ttt (i Int64) ENGINE = MergeTree() ORDER BY i SETTINGS index_granularity = 16, write_final_mark = 0;
+INSERT INTO ttt SELECT number FROM numbers(128);
+OPTIMIZE TABLE ttt;
+```
+
+Запрос:
+
+```sql
+EXPLAIN ESTIMATE SELECT * FROM ttt;
+```
+
+Результат:
+
+```text
+┌─database─┬─table─┬─parts─┬─rows─┬─marks─┐
+│ default  │ ttt   │     1 │  128 │     8 │
+└──────────┴───────┴───────┴──────┴───────┘
+```
+
 [Оригинальная статья](https://clickhouse.tech/docs/ru/sql-reference/statements/explain/) <!--hide-->