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Merge pull request #27536 from adevyatova/annadevyatova-DOCSUP-11968-explain
DOCSUP-11968: Document the SQL-statement EXPLAIN ESTIMATE
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---
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toc_priority: 36
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toc_title: Replicated
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---
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# [experimental] Replicated {#replicated}
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# [experimental] Replicated {#replicated}
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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.
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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.
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@ -384,5 +384,32 @@ ExpressionTransform
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(ReadFromStorage)
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(ReadFromStorage)
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NumbersMt × 2 0 → 1
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NumbersMt × 2 0 → 1
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```
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```
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### EXPLAIN ESTIMATE {#explain-estimate}
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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.
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**Example**
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Creating a table:
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```sql
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CREATE TABLE ttt (i Int64) ENGINE = MergeTree() ORDER BY i SETTINGS index_granularity = 16, write_final_mark = 0;
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INSERT INTO ttt SELECT number FROM numbers(128);
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OPTIMIZE TABLE ttt;
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```
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Query:
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```sql
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EXPLAIN ESTIMATE SELECT * FROM ttt;
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```
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Result:
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```text
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┌─database─┬─table─┬─parts─┬─rows─┬─marks─┐
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│ default │ ttt │ 1 │ 128 │ 8 │
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└──────────┴───────┴───────┴──────┴───────┘
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```
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[Оriginal article](https://clickhouse.tech/docs/en/sql-reference/statements/explain/) <!--hide-->
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[Оriginal article](https://clickhouse.tech/docs/en/sql-reference/statements/explain/) <!--hide-->
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@ -1,3 +1,7 @@
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---
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toc_priority: 36
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toc_title: Replicated
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---
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# [экспериментальный] Replicated {#replicated}
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# [экспериментальный] Replicated {#replicated}
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NumbersMt × 2 0 → 1
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NumbersMt × 2 0 → 1
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```
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```
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### EXPLAIN ESTIMATE {#explain-estimate}
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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).
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**Пример**
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Создадим таблицу:
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```sql
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CREATE TABLE ttt (i Int64) ENGINE = MergeTree() ORDER BY i SETTINGS index_granularity = 16, write_final_mark = 0;
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INSERT INTO ttt SELECT number FROM numbers(128);
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OPTIMIZE TABLE ttt;
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```
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Запрос:
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```sql
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EXPLAIN ESTIMATE SELECT * FROM ttt;
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```
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Результат:
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```text
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┌─database─┬─table─┬─parts─┬─rows─┬─marks─┐
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│ default │ ttt │ 1 │ 128 │ 8 │
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└──────────┴───────┴───────┴──────┴───────┘
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```
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[Оригинальная статья](https://clickhouse.tech/docs/ru/sql-reference/statements/explain/) <!--hide-->
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[Оригинальная статья](https://clickhouse.tech/docs/ru/sql-reference/statements/explain/) <!--hide-->
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