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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
— Atuple
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
tupleHammingDistance
Returns the Hamming Distance between two tuples of the same size.
Syntax
tupleHammingDistance(tuple1, tuple2)
Arguments
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 T
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)] │
└───────────────────────────────────────┘