ClickHouse/docs/en/sql-reference/functions/tuple-functions.md

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66	Tuples

Functions for Working with Tuples

tuple

A function that allows grouping multiple columns. For columns with the types T1, T2, …, it returns a Tuple(T1, T2, …) type tuple containing these columns. There is no cost to execute the function. Tuples are normally used as intermediate values for an argument of IN operators, or for creating a list of formal parameters of lambda functions. Tuples can’t be written to a table.

The function implements the operator (x, y, …).

Syntax

tuple(x, y, …)

tupleElement

A function that allows getting a column from a tuple. ‘N’ is the column index, starting from 1. N must be a constant. ‘N’ must be a constant. ‘N’ must be a strict postive integer no greater than the size of the tuple. There is no cost to execute the function.

The function implements the operator x.N.

Syntax

tupleElement(tuple, n)

untuple

Performs syntactic substitution of tuple elements in the call location.

Syntax

untuple(x)

You can use the EXCEPT expression to skip columns as a result of the query.

Arguments

• x — A tuple function, column, or tuple of elements. Tuple.

Returned value

• None.

Examples

Input table:

┌─key─┬─v1─┬─v2─┬─v3─┬─v4─┬─v5─┬─v6────────┐
│   1 │ 10 │ 20 │ 40 │ 30 │ 15 │ (33,'ab') │
│   2 │ 25 │ 65 │ 70 │ 40 │  6 │ (44,'cd') │
│   3 │ 57 │ 30 │ 20 │ 10 │  5 │ (55,'ef') │
│   4 │ 55 │ 12 │  7 │ 80 │ 90 │ (66,'gh') │
│   5 │ 30 │ 50 │ 70 │ 25 │ 55 │ (77,'kl') │
└─────┴────┴────┴────┴────┴────┴───────────┘

Example of using a Tuple-type column as the untuple function parameter:

Query:

SELECT untuple(v6) FROM kv;

Result:

┌─_ut_1─┬─_ut_2─┐
│    33 │ ab    │
│    44 │ cd    │
│    55 │ ef    │
│    66 │ gh    │
│    77 │ kl    │
└───────┴───────┘

Note: the names are implementation specific and are subject to change. You should not assume specific names of the columns after application of the untuple.

Example of using an EXCEPT expression:

Query:

SELECT untuple((* EXCEPT (v2, v3),)) FROM kv;

Result:

┌─key─┬─v1─┬─v4─┬─v5─┬─v6────────┐
│   1 │ 10 │ 30 │ 15 │ (33,'ab') │
│   2 │ 25 │ 40 │  6 │ (44,'cd') │
│   3 │ 57 │ 10 │  5 │ (55,'ef') │
│   4 │ 55 │ 80 │ 90 │ (66,'gh') │
│   5 │ 30 │ 25 │ 55 │ (77,'kl') │
└─────┴────┴────┴────┴───────────┘

See Also

• Tuple

tupleHammingDistance

Returns the Hamming Distance between two tuples of the same size.

Syntax

tupleHammingDistance(tuple1, tuple2)

Arguments

• tuple1 — First tuple. Tuple.
• tuple2 — Second tuple. Tuple.

Tuples should have the same type of the elements.

Returned value

• The Hamming distance.

Type: UInt8.

Examples

Query:

SELECT tupleHammingDistance((1, 2, 3), (3, 2, 1)) AS HammingDistance;

Result:

┌─HammingDistance─┐
│               2 │
└─────────────────┘

Can be used with MinHash functions for detection of semi-duplicate strings:

SELECT tupleHammingDistance(wordShingleMinHash(string), wordShingleMinHashCaseInsensitive(string)) as HammingDistance FROM (SELECT 'ClickHouse is a column-oriented database management system for online analytical processing of queries.' AS string);

Result:

┌─HammingDistance─┐
│               2 │
└─────────────────┘

tupleToNameValuePairs

Turns a named tuple into an array of (name, value) pairs. For a Tuple(a T, b T, ..., c T) returns Array(Tuple(String, T), ...) in which the Strings represents the named fields of the tuple and the Ts are the values associated with those names. All values in the tuple should be of the same type.

Syntax

tupleToNameValuePairs(tuple)

Arguments

• tuple — Named tuple. Tuple with any type of values.

Returned value

• An array with (name, value) pairs.

Type: Array(Tuple(String, ...)).

Example

Query:

CREATE TABLE tupletest (`col` Tuple(user_ID UInt64, session_ID UInt64) ENGINE = Memory;

INSERT INTO tupletest VALUES (tuple( 100, 2502)), (tuple(1,100));

SELECT tupleToNameValuePairs(col) FROM tupletest;

Result:

┌─tupleToNameValuePairs(col)────────────┐
│ [('user_ID',100),('session_ID',2502)] │
│ [('user_ID',1),('session_ID',100)]    │
└───────────────────────────────────────┘

It is possible to transform colums to rows using this function:

CREATE TABLE tupletest (`col` Tuple(CPU Float64, Memory Float64, Disk Float64)) ENGINE = Memory;

INSERT INTO tupletest VALUES(tuple(3.3, 5.5, 6.6));

SELECT arrayJoin(tupleToNameValuePairs(col))FROM tupletest;

Result:

┌─arrayJoin(tupleToNameValuePairs(col))─┐
│ ('CPU',3.3)                           │
│ ('Memory',5.5)                        │
│ ('Disk',6.6)                          │
└───────────────────────────────────────┘

If you pass a simple tuple to the function, ClickHouse uses the indexes of the values as their names:

SELECT tupleToNameValuePairs(tuple(3, 2, 1));

Result:

┌─tupleToNameValuePairs(tuple(3, 2, 1))─┐
│ [('1',3),('2',2),('3',1)]             │
└───────────────────────────────────────┘