5da33f04c9
* 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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Tuple(T1, T2, ...)
A tuple of elements, each having an individual type.
You can't store tuples in tables (other than Memory tables). They are used for temporary column grouping. Columns can be grouped when an IN expression is used in a query, and for specifying certain formal parameters of lambda functions. For more information, see the sections IN operators and Higher order functions.
Tuples can be the result of a query. In this case, for text formats other than JSON, values are comma-separated in brackets. In JSON formats, tuples are output as arrays (in square brackets).
Creating a tuple
You can use a function to create a tuple:
tuple(T1, T2, ...)
Example of creating a tuple:
:) 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.
Working with data types
When creating a tuple on the fly, ClickHouse automatically detects the type of each argument as the minimum of the types which can store the argument value. If the argument is NULL, the type of the tuple element is Nullable.
Example of automatic data type detection:
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.