DOCSUP-4617: Document the union_default_mode setting #18153
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Задокументировал настройку union_default_mode.
robot-clickhouse
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…-DOCSUP-4617-document_union_default_mode_setting
Изменил заголовок примера.
Убрал лишние символы.
Добавил подраздел в русскую версию, чтобы исправить битую ссылку.
Выполнил перевод на русский язык.
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@akuzm Please, review this PR. |
| @@ -2459,4 +2458,65 @@ Possible values: | |||
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| Default value: `0`. | |||
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| ## union_default_mode {#union-default-mode} | |||
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| Sets a special mode for combining `SELECT` query results using the [UNION](../../sql-reference/statements/select/union-all.md) expression. | |||
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Nothing special with this mode.
| @@ -2459,4 +2458,65 @@ Possible values: | |||
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| Default value: `0`. | |||
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| ## union_default_mode {#union-default-mode} | |||
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| Sets a special mode for combining `SELECT` query results using the [UNION](../../sql-reference/statements/select/union-all.md) expression. | |||
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It should be highlighted that it relates only to UNION without explicit UNION ALL or UNION DISTINCT specification.
| Поддерживается только `UNION ALL`. Обычный `UNION` (`UNION DISTINCT`) не поддерживается. Если вам это нужно `UNION DISTINCT`, вы можете написать `SELECT DISTINCT` из подзапроса, содержащего `UNION ALL`. | ||
| Разница между `UNION ALL` и `UNION DISTINCT` в том, что `UNION DISTINCT` выполняет явное преобразование для результата объединения. Это равнозначно выражению `SELECT DISTINCT` из подзапроса, содержащего `UNION ALL`. | ||
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| # Секция UNION {#union-clause} |
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Надо переписать - пусть будет всё про одну секцию UNION, которая специфицируется с помощью указания ALL или DISTINCT.
Объединил все в один раздел UNION.
Переструктурировал текст.
Подкорректировал английскую и русскую версии.
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@alexey-milovidov Please, review this PR. |
…-DOCSUP-4617-document_union_default_mode_setting
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| Type casting is performed for unions. For example, if two queries being combined have the same field with non-`Nullable` and `Nullable` types from a compatible type, the resulting `UNION` has a `Nullable` type field. | ||
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| Queries that are parts of `UNION` can’t be enclosed in round brackets. [ORDER BY](../../../sql-reference/statements/select/order-by.md) and [LIMIT](../../../sql-reference/statements/select/limit.md) are applied to separate queries, not to the final result. If you need to apply a conversion to the final result, you can put all the queries with `UNION` in a subquery in the [FROM](../../../sql-reference/statements/select/from.md) clause. |
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Now they can.
(SELECT 1 UNION SELECT 2) UNION (SELECT 3 UNION SELECT 2);
Изменил возможность записывать подзапросы с union в круглых скобках.
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@alexey-milovidov Please, check this PR. I fixed it. |
alexey-milovidov
approved these changes
Dec 30, 2020
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Perftect. |
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I decided to make a change in #18615 and has reflected it in the docs. |
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Changelog category:
union_default_mode#16338