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Update doc. [#CLICKHOUSE-5]
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Vitaliy Lyudvichenko
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226d84be09
@ -24,9 +24,6 @@ public:
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private:
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ASTPtr query_ptr;
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Context & context;
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BlockIO executeOnServer(ASTDropQuery & drop);
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BlockIO executeOnCluster(ASTDropQuery & drop);
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};
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@ -1,3 +1,5 @@
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.. _configuration_files:
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Configuration files
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======================
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@ -13,8 +13,10 @@ If "IF NOT EXISTS" is included, the query won't return an error if the database
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CREATE TABLE
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~~~~~~~~~~~~
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The ``CREATE TABLE`` query can have several forms.
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::
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CREATE [TEMPORARY] TABLE [IF NOT EXISTS] [db.]name
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.. code-block:: sql
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CREATE [TEMPORARY] TABLE [IF NOT EXISTS] [db.]name [ON CLUSTER cluster]
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(
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name1 [type1] [DEFAULT|MATERIALIZED|ALIAS expr1],
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name2 [type2] [DEFAULT|MATERIALIZED|ALIAS expr2],
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@ -37,7 +39,7 @@ Creates a table with a structure like the result of the ``SELECT`` query, with t
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In all cases, if IF NOT EXISTS is specified, the query won't return an error if the table already exists. In this case, the query won't do anything.
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Default values
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"""""""""""""""""""""
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""""""""""""""
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The column description can specify an expression for a default value, in one of the following ways:
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``DEFAULT expr``, ``MATERIALIZED expr``, ``ALIAS expr``.
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Example: ``URLDomain String DEFAULT domain(URL)``.
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@ -73,7 +75,7 @@ If you add a new column to a table but later change its default expression, the
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It is not possible to set default values for elements in nested data structures.
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Temporary tables
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"""""""""""""""""
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""""""""""""""""
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In all cases, if TEMPORARY is specified, a temporary table will be created. Temporary tables have the following characteristics:
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- Temporary tables disappear when the session ends, including if the connection is lost.
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- A temporary table is created with the Memory engine. The other table engines are not supported.
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@ -83,6 +85,20 @@ In all cases, if TEMPORARY is specified, a temporary table will be created. Temp
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In most cases, temporary tables are not created manually, but when using external data for a query, or for distributed (GLOBAL) IN. For more information, see the appropriate sections.
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Distributed DDL queries (section ``ON CLUSTER``)
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""""""""""""""""""""""""""""""""""""""""""""""""
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Queries ``CREATE``, ``DROP``, ``ALTER``, ``RENAME`` support distributed execution on cluster.
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For example, the following query creates ``Distributed`` table ``all_hits`` for each host of the cluster ``cluster``:
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.. code-block:: sql
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CREATE TABLE IF NOT EXISTS all_hits ON CLUSTER cluster (p Date, i Int32) ENGINE = Distributed(cluster, default, hits)
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To correctly execute such queries you need to have equal definitions of the cluster on each host (you can use :ref:`ZooKeeper substitutions <configuration_files>` to syncronize configs on hosts) and connection to ZooKeeper quorum.
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Local version of the query will be eventually executed on each host of the cluster, even if some hosts are temporary unavaiable; on each host queries are executed stictly sequentually.
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At the moment, ``ALTER`` queries for replicated tables are not supported yet.
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CREATE VIEW
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~~~~~~~~~~~~
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``CREATE [MATERIALIZED] VIEW [IF NOT EXISTS] [db.]name [ENGINE = engine] [POPULATE] AS SELECT ...``
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@ -130,13 +146,17 @@ This query is used when starting the server. The server stores table metadata as
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DROP
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~~~~
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This query has two types: ``DROP DATABASE`` and ``DROP TABLE``.
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::
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DROP DATABASE [IF EXISTS] db
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.. code-block:: sql
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DROP DATABASE [IF EXISTS] db [ON CLUSTER cluster]
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Deletes all tables inside the 'db' database, then deletes the 'db' database itself.
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If IF EXISTS is specified, it doesn't return an error if the database doesn't exist.
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::
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DROP TABLE [IF EXISTS] [db.]name
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.. code-block:: sql
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DROP TABLE [IF EXISTS] [db.]name [ON CLUSTER cluster]
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Deletes the table.
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If IF EXISTS is specified, it doesn't return an error if the table doesn't exist or the database doesn't exist.
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@ -154,20 +174,24 @@ There is no DETACH DATABASE query.
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RENAME
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~~~~~~
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Renames one or more tables.
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::
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RENAME TABLE [db11.]name11 TO [db12.]name12, [db21.]name21 TO [db22.]name22, ...
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.. code-block:: sql
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RENAME TABLE [db11.]name11 TO [db12.]name12, [db21.]name21 TO [db22.]name22, ... [ON CLUSTER cluster]
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All tables are renamed under global locking. Renaming tables is a light operation. If you indicated another database after TO, the table will be moved to this database. However, the directories with databases must reside in the same file system (otherwise, an error is returned).
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ALTER
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~~~~~
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The ALTER query is only supported for *MergeTree type tables, as well as for Merge and Distributed types. The query has several variations.
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Column manipulations
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""""""""""""""""""""""""
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Lets you change the table structure.
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::
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ALTER TABLE [db].name ADD|DROP|MODIFY COLUMN ...
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Lets you change the table structure.
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.. code-block:: sql
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ALTER TABLE [db].name [ON CLUSTER cluster] ADD|DROP|MODIFY COLUMN ...
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In the query, specify a list of one or more comma-separated actions. Each action is an operation on a column.
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@ -18,7 +18,7 @@ CREATE TABLE
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.. code-block:: sql
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CREATE [TEMPORARY] TABLE [IF NOT EXISTS] [db.]name
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CREATE [TEMPORARY] TABLE [IF NOT EXISTS] [db.]name [ON CLUSTER cluster]
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(
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name1 [type1] [DEFAULT|MATERIALIZED|ALIAS expr1],
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name2 [type2] [DEFAULT|MATERIALIZED|ALIAS expr2],
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@ -92,6 +92,20 @@ CREATE TABLE
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В большинстве случаев, временные таблицы создаются не вручную, а при использовании внешних данных для запроса, или при распределённом ``(GLOBAL) IN``. Подробнее см. соответствующие разделы
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Распределенные DDL запросы (секция ``ON CLUSTER``)
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""""""""""""""""""""""""""""""""""""""""""""""""""
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Запросы ``CREATE``, ``DROP``, ``ALTER``, ``RENAME`` поддерживают возможность распределенного выполнения на кластере.
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Например, следующий запрос создает ``Distributed``-таблицу ``all_hits`` на каждом хосте кластера ``cluster``:
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.. code-block:: sql
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CREATE TABLE IF NOT EXISTS all_hits ON CLUSTER cluster (p Date, i Int32) ENGINE = Distributed(cluster, default, hits)
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Для корректного выполнения таких запросов необходимо на каждом хосте иметь одинаковое определение кластера (для упрощения синхронизации конфигов можете использовать :ref:`подстановки из ZooKeeper <configurattion_files>`), также необходимо подключение к ZooKeeper серверам.
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Локальная версия запроса в конечном итоге будет выполнена на каждом хосте кластера, даже если некоторые хосты в данный момент не доступны, гарантируется упорядоченность выполнения запросов в рамках одного хоста.
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Пока не поддерживаются ``ALTER``-запросы для реплицированных таблиц.
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CREATE VIEW
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~~~~~~~~~~~~
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@ -152,14 +166,14 @@ DROP
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.. code-block:: sql
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DROP DATABASE [IF EXISTS] db
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DROP DATABASE [IF EXISTS] db [ON CLUSTER cluster]
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Удаляет все таблицы внутри базы данных db, а затем саму базу данных db.
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Если указано ``IF EXISTS`` - не выдавать ошибку, если база данных не существует.
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.. code-block:: sql
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DROP TABLE [IF EXISTS] [db.]name
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DROP TABLE [IF EXISTS] [db.]name [ON CLUSTER cluster]
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Удаляет таблицу.
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Если указано ``IF EXISTS`` - не выдавать ошибку, если таблица не существует или база данных не существует.
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@ -183,7 +197,7 @@ RENAME
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.. code-block:: sql
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RENAME TABLE [db11.]name11 TO [db12.]name12, [db21.]name21 TO [db22.]name22, ...
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RENAME TABLE [db11.]name11 TO [db12.]name12, [db21.]name21 TO [db22.]name22, ... [ON CLUSTER cluster]
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Все таблицы переименовываются под глобальной блокировкой. Переименовывание таблицы является лёгкой операцией. Если вы указали после TO другую базу данных, то таблица будет перенесена в эту базу данных. При этом, директории с базами данных должны быть расположены в одной файловой системе (иначе возвращается ошибка).
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@ -197,7 +211,7 @@ ALTER
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.. code-block:: sql
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ALTER TABLE [db].name ADD|DROP|MODIFY COLUMN ...
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ALTER TABLE [db].name [ON CLUSTER cluster] ADD|DROP|MODIFY COLUMN ...
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В запросе указывается список из одного или более действий через запятую.
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Каждое действие - операция над столбцом.
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