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* Update of english version of descriprion of the table function `file`. * New syntax for ReplacingMergeTree. Some improvements in text. * Significantly change article about SummingMergeTree. Article is restructured, text is changed in many places of the document. New syntax for table creation is described. * Descriptions of AggregateFunction and AggregatingMergeTree are updated. Russian version. * New syntax for new syntax of CREATE TABLE * Added english docs on Aggregating, Replacing and SummingMergeTree. * CollapsingMergeTree docs. English version. * 1. Update of CollapsingMergeTree. 2. Minor changes in markup * Update aggregatefunction.md * Update aggregatefunction.md * Update aggregatefunction.md * Update aggregatingmergetree.md * GraphiteMergeTree docs update. New syntax for creation of Replicated* tables. Minor changes in *MergeTree tables creation syntax. * Markup fix * Markup and language fixes * Clarification in the CollapsingMergeTree article * DOCAPI-4821. Sync between ru and en versions of docs. * Fixed the ambiguity in geo functions description. * Example of JOIN in ru docs * Deleted misinforming example. * Fixed links to IN operators.
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1.9 KiB
Tuple(T1, T2, ...)
元组，其中每个元素都有单独的 类型。
不能在表中存储元组（除了内存表）。它们可以用于临时列分组。在查询中，IN 表达式和带特定参数的 lambda 函数可以来对临时列进行分组。更多信息，请参阅 IN 操作符 and Higher order functions。
元组可以是查询的结果。在这种情况下，对于JSON以外的文本格式，括号中的值是逗号分隔的。在JSON格式中，元组作为数组输出（在方括号中）。
创建元组
可以使用函数来创建元组：
tuple(T1, T2, ...)
创建元组的示例：
:) SELECT tuple(1,'a') AS x, toTypeName(x)
SELECT
(1, 'a') AS x,
toTypeName(x)
┌─x───────┬─toTypeName(tuple(1, 'a'))─┐
│ (1,'a') │ Tuple(UInt8, String) │
└─────────┴───────────────────────────┘
1 rows in set. Elapsed: 0.021 sec.
元组中的数据类型
在动态创建元组时，ClickHouse 会自动为元组的每一个参数赋予最小可表达的类型。如果参数为 NULL，那这个元组对应元素是 Nullable。
自动数据类型检测示例：
SELECT tuple(1, NULL) AS x, toTypeName(x)
SELECT
(1, NULL) AS x,
toTypeName(x)
┌─x────────┬─toTypeName(tuple(1, NULL))──────┐
│ (1,NULL) │ Tuple(UInt8, Nullable(Nothing)) │
└──────────┴─────────────────────────────────┘
1 rows in set. Elapsed: 0.002 sec.