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

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/en/sql-reference/functions/array-functions	10	Arrays

Array Functions

empty

Checks whether the input array is empty.

Syntax

empty([x])

An array is considered empty if it does not contain any elements.

:::note Can be optimized by enabling the optimize_functions_to_subcolumns setting. With optimize_functions_to_subcolumns = 1 the function reads only size0 subcolumn instead of reading and processing the whole array column. The query SELECT empty(arr) FROM TABLE; transforms to SELECT arr.size0 = 0 FROM TABLE;. :::

The function also works for strings or UUID.

Arguments

• [x] — Input array. Array.

Returned value

• Returns 1 for an empty array or 0 for a non-empty array.

Type: UInt8.

Example

Query:

SELECT empty([]);

Result:

┌─empty(array())─┐
│              1 │
└────────────────┘

notEmpty

Checks whether the input array is non-empty.

Syntax

notEmpty([x])

An array is considered non-empty if it contains at least one element.

:::note Can be optimized by enabling the optimize_functions_to_subcolumns setting. With optimize_functions_to_subcolumns = 1 the function reads only size0 subcolumn instead of reading and processing the whole array column. The query SELECT notEmpty(arr) FROM table transforms to SELECT arr.size0 != 0 FROM TABLE. :::

The function also works for strings or UUID.

Arguments

• [x] — Input array. Array.

Returned value

• Returns 1 for a non-empty array or 0 for an empty array.

Type: UInt8.

Example

Query:

SELECT notEmpty([1,2]);

Result:

┌─notEmpty([1, 2])─┐
│                1 │
└──────────────────┘

length

Returns the number of items in the array. The result type is UInt64. The function also works for strings.

Can be optimized by enabling the optimize_functions_to_subcolumns setting. With optimize_functions_to_subcolumns = 1 the function reads only size0 subcolumn instead of reading and processing the whole array column. The query SELECT length(arr) FROM table transforms to SELECT arr.size0 FROM TABLE.

emptyArrayUInt8, emptyArrayUInt16, emptyArrayUInt32, emptyArrayUInt64

emptyArrayInt8, emptyArrayInt16, emptyArrayInt32, emptyArrayInt64

emptyArrayFloat32, emptyArrayFloat64

emptyArrayDate, emptyArrayDateTime

emptyArrayString

Accepts zero arguments and returns an empty array of the appropriate type.

emptyArrayToSingle

Accepts an empty array and returns a one-element array that is equal to the default value.

range(end), range([start, ] end [, step])

Returns an array of numbers from start to end - 1 by step. The supported types are UInt8, UInt16, UInt32, UInt64, Int8, Int16, Int32, Int64.

Syntax

range([start, ] end [, step])

Arguments

• start — The first element of the array. Optional, required if step is used. Default value: 0.
• end — The number before which the array is constructed. Required.
• step — Determines the incremental step between each element in the array. Optional. Default value: 1.

Returned value

• Array of numbers from start to end - 1 by step.

Implementation details

• All arguments start, end, step must be below data types: UInt8, UInt16, UInt32, UInt64,Int8, Int16, Int32, Int64, as well as elements of the returned array, which's type is a super type of all arguments's.
• An exception is thrown if query results in arrays with a total length of more than number of elements specified by the function_range_max_elements_in_block setting.

Examples

Query:

SELECT range(5), range(1, 5), range(1, 5, 2), range(-1, 5, 2);

Result:

┌─range(5)────┬─range(1, 5)─┬─range(1, 5, 2)─┬─range(-1, 5, 2)─┐
│ [0,1,2,3,4] │ [1,2,3,4]   │ [1,3]          │ [-1,1,3]        │
└─────────────┴─────────────┴────────────────┴─────────────────┘

array(x1, …), operator [x1, …]

Creates an array from the function arguments. The arguments must be constants and have types that have the smallest common type. At least one argument must be passed, because otherwise it isn’t clear which type of array to create. That is, you can’t use this function to create an empty array (to do that, use the ‘emptyArray*’ function described above). Returns an ‘Array(T)’ type result, where ‘T’ is the smallest common type out of the passed arguments.

arrayWithConstant(length, elem)

Creates an array of length length filled with the constant elem.

arrayConcat

Combines arrays passed as arguments.

arrayConcat(arrays)

Arguments

• arrays – Arbitrary number of arguments of Array type. Example

SELECT arrayConcat([1, 2], [3, 4], [5, 6]) AS res

┌─res───────────┐
│ [1,2,3,4,5,6] │
└───────────────┘

arrayElement(arr, n), operator arr[n]

Get the element with the index n from the array arr. n must be any integer type. Indexes in an array begin from one. Negative indexes are supported. In this case, it selects the corresponding element numbered from the end. For example, arr[-1] is the last item in the array.

If the index falls outside of the bounds of an array, it returns some default value (0 for numbers, an empty string for strings, etc.), except for the case with a non-constant array and a constant index 0 (in this case there will be an error Array indices are 1-based).

has(arr, elem)

Checks whether the ‘arr’ array has the ‘elem’ element. Returns 0 if the element is not in the array, or 1 if it is.

NULL is processed as a value.

SELECT has([1, 2, NULL], NULL)

┌─has([1, 2, NULL], NULL)─┐
│                       1 │
└─────────────────────────┘

hasAll

Checks whether one array is a subset of another.

hasAll(set, subset)

Arguments

• set – Array of any type with a set of elements.
• subset – Array of any type with elements that should be tested to be a subset of set.

Return values

• 1, if set contains all of the elements from subset.
• 0, otherwise.

Peculiar properties

• An empty array is a subset of any array.
• Null processed as a value.
• Order of values in both of arrays does not matter.

Examples

SELECT hasAll([], []) returns 1.

SELECT hasAll([1, Null], [Null]) returns 1.

SELECT hasAll([1.0, 2, 3, 4], [1, 3]) returns 1.

SELECT hasAll(['a', 'b'], ['a']) returns 1.

SELECT hasAll([1], ['a']) returns 0.

SELECT hasAll([[1, 2], [3, 4]], [[1, 2], [3, 5]]) returns 0.

hasAny

Checks whether two arrays have intersection by some elements.

hasAny(array1, array2)

Arguments

• array1 – Array of any type with a set of elements.
• array2 – Array of any type with a set of elements.

Return values

• 1, if array1 and array2 have one similar element at least.
• 0, otherwise.

Peculiar properties

• Null processed as a value.
• Order of values in both of arrays does not matter.

Examples

SELECT hasAny([1], []) returns 0.

SELECT hasAny([Null], [Null, 1]) returns 1.

SELECT hasAny([-128, 1., 512], [1]) returns 1.

SELECT hasAny([[1, 2], [3, 4]], ['a', 'c']) returns 0.

SELECT hasAll([[1, 2], [3, 4]], [[1, 2], [1, 2]]) returns 1.

hasSubstr

Checks whether all the elements of array2 appear in array1 in the same exact order. Therefore, the function will return 1, if and only if array1 = prefix + array2 + suffix.

hasSubstr(array1, array2)

In other words, the functions will check whether all the elements of array2 are contained in array1 like the hasAll function. In addition, it will check that the elements are observed in the same order in both array1 and array2.

For Example:

• hasSubstr([1,2,3,4], [2,3]) returns 1. However, hasSubstr([1,2,3,4], [3,2]) will return 0.
• hasSubstr([1,2,3,4], [1,2,3]) returns 1. However, hasSubstr([1,2,3,4], [1,2,4]) will return 0.

Arguments

• array1 – Array of any type with a set of elements.
• array2 – Array of any type with a set of elements.

Return values

• 1, if array1 contains array2.
• 0, otherwise.

Peculiar properties

• The function will return 1 if array2 is empty.
• Null processed as a value. In other words hasSubstr([1, 2, NULL, 3, 4], [2,3]) will return 0. However, hasSubstr([1, 2, NULL, 3, 4], [2,NULL,3]) will return 1
• Order of values in both of arrays does matter.

Examples

SELECT hasSubstr([], []) returns 1.

SELECT hasSubstr([1, Null], [Null]) returns 1.

SELECT hasSubstr([1.0, 2, 3, 4], [1, 3]) returns 0.

SELECT hasSubstr(['a', 'b'], ['a']) returns 1.

SELECT hasSubstr(['a', 'b' , 'c'], ['a', 'b']) returns 1.

SELECT hasSubstr(['a', 'b' , 'c'], ['a', 'c']) returns 0.

SELECT hasSubstr([[1, 2], [3, 4], [5, 6]], [[1, 2], [3, 4]]) returns 1.

indexOf(arr, x)

Returns the index of the first ‘x’ element (starting from 1) if it is in the array, or 0 if it is not.

Example:

SELECT indexOf([1, 3, NULL, NULL], NULL)

┌─indexOf([1, 3, NULL, NULL], NULL)─┐
│                                 3 │
└───────────────────────────────────┘

Elements set to NULL are handled as normal values.

arrayCount([func,] arr1, …)

Returns the number of elements for which func(arr1[i], …, arrN[i]) returns something other than 0. If func is not specified, it returns the number of non-zero elements in the array.

Note that the arrayCount is a higher-order function. You can pass a lambda function to it as the first argument.

countEqual(arr, x)

Returns the number of elements in the array equal to x. Equivalent to arrayCount (elem -> elem = x, arr).

NULL elements are handled as separate values.

Example:

SELECT countEqual([1, 2, NULL, NULL], NULL)

┌─countEqual([1, 2, NULL, NULL], NULL)─┐
│                                    2 │
└──────────────────────────────────────┘

arrayEnumerate(arr)

Returns the array [1, 2, 3, …, length (arr) ]

This function is normally used with ARRAY JOIN. It allows counting something just once for each array after applying ARRAY JOIN. Example:

SELECT
    count() AS Reaches,
    countIf(num = 1) AS Hits
FROM test.hits
ARRAY JOIN
    GoalsReached,
    arrayEnumerate(GoalsReached) AS num
WHERE CounterID = 160656
LIMIT 10

┌─Reaches─┬──Hits─┐
│   95606 │ 31406 │
└─────────┴───────┘

In this example, Reaches is the number of conversions (the strings received after applying ARRAY JOIN), and Hits is the number of pageviews (strings before ARRAY JOIN). In this particular case, you can get the same result in an easier way:

SELECT
    sum(length(GoalsReached)) AS Reaches,
    count() AS Hits
FROM test.hits
WHERE (CounterID = 160656) AND notEmpty(GoalsReached)

┌─Reaches─┬──Hits─┐
│   95606 │ 31406 │
└─────────┴───────┘

This function can also be used in higher-order functions. For example, you can use it to get array indexes for elements that match a condition.

arrayEnumerateUniq(arr, …)

Returns an array the same size as the source array, indicating for each element what its position is among elements with the same value. For example: arrayEnumerateUniq([10, 20, 10, 30]) = [1, 1, 2, 1].

This function is useful when using ARRAY JOIN and aggregation of array elements. Example:

SELECT
    Goals.ID AS GoalID,
    sum(Sign) AS Reaches,
    sumIf(Sign, num = 1) AS Visits
FROM test.visits
ARRAY JOIN
    Goals,
    arrayEnumerateUniq(Goals.ID) AS num
WHERE CounterID = 160656
GROUP BY GoalID
ORDER BY Reaches DESC
LIMIT 10

┌──GoalID─┬─Reaches─┬─Visits─┐
│   53225 │    3214 │   1097 │
│ 2825062 │    3188 │   1097 │
│   56600 │    2803 │    488 │
│ 1989037 │    2401 │    365 │
│ 2830064 │    2396 │    910 │
│ 1113562 │    2372 │    373 │
│ 3270895 │    2262 │    812 │
│ 1084657 │    2262 │    345 │
│   56599 │    2260 │    799 │
│ 3271094 │    2256 │    812 │
└─────────┴─────────┴────────┘

In this example, each goal ID has a calculation of the number of conversions (each element in the Goals nested data structure is a goal that was reached, which we refer to as a conversion) and the number of sessions. Without ARRAY JOIN, we would have counted the number of sessions as sum(Sign). But in this particular case, the rows were multiplied by the nested Goals structure, so in order to count each session one time after this, we apply a condition to the value of the arrayEnumerateUniq(Goals.ID) function.

The arrayEnumerateUniq function can take multiple arrays of the same size as arguments. In this case, uniqueness is considered for tuples of elements in the same positions in all the arrays.

SELECT arrayEnumerateUniq([1, 1, 1, 2, 2, 2], [1, 1, 2, 1, 1, 2]) AS res

┌─res───────────┐
│ [1,2,1,1,2,1] │
└───────────────┘

This is necessary when using ARRAY JOIN with a nested data structure and further aggregation across multiple elements in this structure.

arrayPopBack

Removes the last item from the array.

arrayPopBack(array)

Arguments

• array – Array.

Example

SELECT arrayPopBack([1, 2, 3]) AS res;

┌─res───┐
│ [1,2] │
└───────┘

arrayPopFront

Removes the first item from the array.

arrayPopFront(array)

Arguments

• array – Array.

Example

SELECT arrayPopFront([1, 2, 3]) AS res;

┌─res───┐
│ [2,3] │
└───────┘

arrayPushBack

Adds one item to the end of the array.

arrayPushBack(array, single_value)

Arguments

• array – Array.
• single_value – A single value. Only numbers can be added to an array with numbers, and only strings can be added to an array of strings. When adding numbers, ClickHouse automatically sets the single_value type for the data type of the array. For more information about the types of data in ClickHouse, see “Data types”. Can be NULL. The function adds a NULL element to an array, and the type of array elements converts to Nullable.

Example

SELECT arrayPushBack(['a'], 'b') AS res;

┌─res───────┐
│ ['a','b'] │
└───────────┘

arrayPushFront

Adds one element to the beginning of the array.

arrayPushFront(array, single_value)

Arguments

• array – Array.
• single_value – A single value. Only numbers can be added to an array with numbers, and only strings can be added to an array of strings. When adding numbers, ClickHouse automatically sets the single_value type for the data type of the array. For more information about the types of data in ClickHouse, see “Data types”. Can be NULL. The function adds a NULL element to an array, and the type of array elements converts to Nullable.

Example

SELECT arrayPushFront(['b'], 'a') AS res;

┌─res───────┐
│ ['a','b'] │
└───────────┘

arrayResize

Changes the length of the array.

arrayResize(array, size[, extender])

Arguments:

• array — Array.
• size — Required length of the array.
  • If size is less than the original size of the array, the array is truncated from the right.
• If size is larger than the initial size of the array, the array is extended to the right with extender values or default values for the data type of the array items.
• extender — Value for extending an array. Can be NULL.

Returned value:

An array of length size.

Examples of calls

SELECT arrayResize([1], 3);

┌─arrayResize([1], 3)─┐
│ [1,0,0]             │
└─────────────────────┘

SELECT arrayResize([1], 3, NULL);

┌─arrayResize([1], 3, NULL)─┐
│ [1,NULL,NULL]             │
└───────────────────────────┘

arraySlice

Returns a slice of the array.

arraySlice(array, offset[, length])

Arguments

• array – Array of data.
• offset – Indent from the edge of the array. A positive value indicates an offset on the left, and a negative value is an indent on the right. Numbering of the array items begins with 1.
• length – The length of the required slice. If you specify a negative value, the function returns an open slice [offset, array_length - length]. If you omit the value, the function returns the slice [offset, the_end_of_array].

Example

SELECT arraySlice([1, 2, NULL, 4, 5], 2, 3) AS res;

┌─res────────┐
│ [2,NULL,4] │
└────────────┘

Array elements set to NULL are handled as normal values.

arraySort([func,] arr, …)

Sorts the elements of the arr array in ascending order. If the func function is specified, sorting order is determined by the result of the func function applied to the elements of the array. If func accepts multiple arguments, the arraySort function is passed several arrays that the arguments of func will correspond to. Detailed examples are shown at the end of arraySort description.

Example of integer values sorting:

SELECT arraySort([1, 3, 3, 0]);

┌─arraySort([1, 3, 3, 0])─┐
│ [0,1,3,3]               │
└─────────────────────────┘

Example of string values sorting:

SELECT arraySort(['hello', 'world', '!']);

┌─arraySort(['hello', 'world', '!'])─┐
│ ['!','hello','world']              │
└────────────────────────────────────┘

Consider the following sorting order for the NULL, NaN and Inf values:

SELECT arraySort([1, nan, 2, NULL, 3, nan, -4, NULL, inf, -inf]);

┌─arraySort([1, nan, 2, NULL, 3, nan, -4, NULL, inf, -inf])─┐
│ [-inf,-4,1,2,3,inf,nan,nan,NULL,NULL]                     │
└───────────────────────────────────────────────────────────┘

• -Inf values are first in the array.
• NULL values are last in the array.
• NaN values are right before NULL.
• Inf values are right before NaN.

Note that arraySort is a higher-order function. You can pass a lambda function to it as the first argument. In this case, sorting order is determined by the result of the lambda function applied to the elements of the array.

Let’s consider the following example:

SELECT arraySort((x) -> -x, [1, 2, 3]) as res;

┌─res─────┐
│ [3,2,1] │
└─────────┘

For each element of the source array, the lambda function returns the sorting key, that is, [1 –> -1, 2 –> -2, 3 –> -3]. Since the arraySort function sorts the keys in ascending order, the result is [3, 2, 1]. Thus, the (x) –> -x lambda function sets the descending order in a sorting.

The lambda function can accept multiple arguments. In this case, you need to pass the arraySort function several arrays of identical length that the arguments of lambda function will correspond to. The resulting array will consist of elements from the first input array; elements from the next input array(s) specify the sorting keys. For example:

SELECT arraySort((x, y) -> y, ['hello', 'world'], [2, 1]) as res;

┌─res────────────────┐
│ ['world', 'hello'] │
└────────────────────┘

Here, the elements that are passed in the second array ([2, 1]) define a sorting key for the corresponding element from the source array ([‘hello’, ‘world’]), that is, [‘hello’ –> 2, ‘world’ –> 1]. Since the lambda function does not use x, actual values of the source array do not affect the order in the result. So, ‘hello’ will be the second element in the result, and ‘world’ will be the first.

Other examples are shown below.

SELECT arraySort((x, y) -> y, [0, 1, 2], ['c', 'b', 'a']) as res;

┌─res─────┐
│ [2,1,0] │
└─────────┘

SELECT arraySort((x, y) -> -y, [0, 1, 2], [1, 2, 3]) as res;

┌─res─────┐
│ [2,1,0] │
└─────────┘

:::note To improve sorting efficiency, the Schwartzian transform is used. :::

arrayReverseSort([func,] arr, …)

Sorts the elements of the arr array in descending order. If the func function is specified, arr is sorted according to the result of the func function applied to the elements of the array, and then the sorted array is reversed. If func accepts multiple arguments, the arrayReverseSort function is passed several arrays that the arguments of func will correspond to. Detailed examples are shown at the end of arrayReverseSort description.

Example of integer values sorting:

SELECT arrayReverseSort([1, 3, 3, 0]);

┌─arrayReverseSort([1, 3, 3, 0])─┐
│ [3,3,1,0]                      │
└────────────────────────────────┘

Example of string values sorting:

SELECT arrayReverseSort(['hello', 'world', '!']);

┌─arrayReverseSort(['hello', 'world', '!'])─┐
│ ['world','hello','!']                     │
└───────────────────────────────────────────┘

Consider the following sorting order for the NULL, NaN and Inf values:

SELECT arrayReverseSort([1, nan, 2, NULL, 3, nan, -4, NULL, inf, -inf]) as res;

┌─res───────────────────────────────────┐
│ [inf,3,2,1,-4,-inf,nan,nan,NULL,NULL] │
└───────────────────────────────────────┘

• Inf values are first in the array.
• NULL values are last in the array.
• NaN values are right before NULL.
• -Inf values are right before NaN.

Note that the arrayReverseSort is a higher-order function. You can pass a lambda function to it as the first argument. Example is shown below.

SELECT arrayReverseSort((x) -> -x, [1, 2, 3]) as res;

┌─res─────┐
│ [1,2,3] │
└─────────┘

The array is sorted in the following way:

1. At first, the source array ([1, 2, 3]) is sorted according to the result of the lambda function applied to the elements of the array. The result is an array [3, 2, 1].
2. Array that is obtained on the previous step, is reversed. So, the final result is [1, 2, 3].

The lambda function can accept multiple arguments. In this case, you need to pass the arrayReverseSort function several arrays of identical length that the arguments of lambda function will correspond to. The resulting array will consist of elements from the first input array; elements from the next input array(s) specify the sorting keys. For example:

SELECT arrayReverseSort((x, y) -> y, ['hello', 'world'], [2, 1]) as res;

┌─res───────────────┐
│ ['hello','world'] │
└───────────────────┘

In this example, the array is sorted in the following way:

1. At first, the source array ([‘hello’, ‘world’]) is sorted according to the result of the lambda function applied to the elements of the arrays. The elements that are passed in the second array ([2, 1]), define the sorting keys for corresponding elements from the source array. The result is an array [‘world’, ‘hello’].
2. Array that was sorted on the previous step, is reversed. So, the final result is [‘hello’, ‘world’].

Other examples are shown below.

SELECT arrayReverseSort((x, y) -> y, [4, 3, 5], ['a', 'b', 'c']) AS res;

┌─res─────┐
│ [5,3,4] │
└─────────┘

SELECT arrayReverseSort((x, y) -> -y, [4, 3, 5], [1, 2, 3]) AS res;

┌─res─────┐
│ [4,3,5] │
└─────────┘

arrayUniq(arr, …)

If one argument is passed, it counts the number of different elements in the array. If multiple arguments are passed, it counts the number of different tuples of elements at corresponding positions in multiple arrays.

If you want to get a list of unique items in an array, you can use arrayReduce(‘groupUniqArray’, arr).

arrayJoin(arr)

A special function. See the section “ArrayJoin function”.

arrayDifference

Calculates an array of differences between adjacent array elements. The first element of the result array will be 0, the second a[1] - a[0], the third a[2] - a[1], etc. The type of elements in the result array is determined by the type inference rules for subtraction (e.g. UInt8 - UInt8 = Int16).

Syntax

arrayDifference(array)

Arguments

• array – Array.

Returned values

Returns an array of differences between adjacent array elements.

Type: UInt*, Int*, Float*.

Example

Query:

SELECT arrayDifference([1, 2, 3, 4]);

Result:

┌─arrayDifference([1, 2, 3, 4])─┐
│ [0,1,1,1]                     │
└───────────────────────────────┘

Example of the overflow due to result type Int64:

Query:

SELECT arrayDifference([0, 10000000000000000000]);

Result:

┌─arrayDifference([0, 10000000000000000000])─┐
│ [0,-8446744073709551616]                   │
└────────────────────────────────────────────┘

arrayDistinct

Takes an array, returns an array containing the distinct elements only.

Syntax

arrayDistinct(array)

Arguments

• array – Array.

Returned values

Returns an array containing the distinct elements.

Example

Query:

SELECT arrayDistinct([1, 2, 2, 3, 1]);

Result:

┌─arrayDistinct([1, 2, 2, 3, 1])─┐
│ [1,2,3]                        │
└────────────────────────────────┘

arrayEnumerateDense(arr)

Returns an array of the same size as the source array, indicating where each element first appears in the source array.

Example:

SELECT arrayEnumerateDense([10, 20, 10, 30])

┌─arrayEnumerateDense([10, 20, 10, 30])─┐
│ [1,2,1,3]                             │
└───────────────────────────────────────┘

arrayIntersect(arr)

Takes multiple arrays, returns an array with elements that are present in all source arrays.

Example:

SELECT
    arrayIntersect([1, 2], [1, 3], [2, 3]) AS no_intersect,
    arrayIntersect([1, 2], [1, 3], [1, 4]) AS intersect

┌─no_intersect─┬─intersect─┐
│ []           │ [1]       │
└──────────────┴───────────┘

arrayReduce

Applies an aggregate function to array elements and returns its result. The name of the aggregation function is passed as a string in single quotes 'max', 'sum'. When using parametric aggregate functions, the parameter is indicated after the function name in parentheses 'uniqUpTo(6)'.

Syntax

arrayReduce(agg_func, arr1, arr2, ..., arrN)

Arguments

• agg_func — The name of an aggregate function which should be a constant string.
• arr — Any number of array type columns as the parameters of the aggregation function.

Returned value

Example

Query:

SELECT arrayReduce('max', [1, 2, 3]);

Result:

┌─arrayReduce('max', [1, 2, 3])─┐
│                             3 │
└───────────────────────────────┘

If an aggregate function takes multiple arguments, then this function must be applied to multiple arrays of the same size.

Query:

SELECT arrayReduce('maxIf', [3, 5], [1, 0]);

Result:

┌─arrayReduce('maxIf', [3, 5], [1, 0])─┐
│                                    3 │
└──────────────────────────────────────┘

Example with a parametric aggregate function:

Query:

SELECT arrayReduce('uniqUpTo(3)', [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]);

Result:

┌─arrayReduce('uniqUpTo(3)', [1, 2, 3, 4, 5, 6, 7, 8, 9, 10])─┐
│                                                           4 │
└─────────────────────────────────────────────────────────────┘

arrayReduceInRanges

Applies an aggregate function to array elements in given ranges and returns an array containing the result corresponding to each range. The function will return the same result as multiple arrayReduce(agg_func, arraySlice(arr1, index, length), ...).

Syntax

arrayReduceInRanges(agg_func, ranges, arr1, arr2, ..., arrN)

Arguments

• agg_func — The name of an aggregate function which should be a constant string.
• ranges — The ranges to aggretate which should be an array of tuples which containing the index and the length of each range.
• arr — Any number of Array type columns as the parameters of the aggregation function.

Returned value

• Array containing results of the aggregate function over specified ranges.

Type: Array.

Example

Query:

SELECT arrayReduceInRanges(
    'sum',
    [(1, 5), (2, 3), (3, 4), (4, 4)],
    [1000000, 200000, 30000, 4000, 500, 60, 7]
) AS res

Result:

┌─res─────────────────────────┐
│ [1234500,234000,34560,4567] │
└─────────────────────────────┘

arrayReverse(arr)

Returns an array of the same size as the original array containing the elements in reverse order.

Example:

SELECT arrayReverse([1, 2, 3])

┌─arrayReverse([1, 2, 3])─┐
│ [3,2,1]                 │
└─────────────────────────┘

reverse(arr)

Synonym for “arrayReverse”

arrayFlatten

Converts an array of arrays to a flat array.

Function:

• Applies to any depth of nested arrays.
• Does not change arrays that are already flat.

The flattened array contains all the elements from all source arrays.

Syntax

flatten(array_of_arrays)

Alias: flatten.

Arguments

• array_of_arrays — Array of arrays. For example, [[1,2,3], [4,5]].

Examples

SELECT flatten([[[1]], [[2], [3]]]);

┌─flatten(array(array([1]), array([2], [3])))─┐
│ [1,2,3]                                     │
└─────────────────────────────────────────────┘

arrayCompact

Removes consecutive duplicate elements from an array. The order of result values is determined by the order in the source array.

Syntax

arrayCompact(arr)

Arguments

arr — The array to inspect.

Returned value

The array without duplicate.

Type: Array.

Example

Query:

SELECT arrayCompact([1, 1, nan, nan, 2, 3, 3, 3]);

Result:

┌─arrayCompact([1, 1, nan, nan, 2, 3, 3, 3])─┐
│ [1,nan,nan,2,3]                            │
└────────────────────────────────────────────┘

arrayZip

Combines multiple arrays into a single array. The resulting array contains the corresponding elements of the source arrays grouped into tuples in the listed order of arguments.

Syntax

arrayZip(arr1, arr2, ..., arrN)

Arguments

• arrN — Array.

The function can take any number of arrays of different types. All the input arrays must be of equal size.

Returned value

• Array with elements from the source arrays grouped into tuples. Data types in the tuple are the same as types of the input arrays and in the same order as arrays are passed.

Type: Array.

Example

Query:

SELECT arrayZip(['a', 'b', 'c'], [5, 2, 1]);

Result:

┌─arrayZip(['a', 'b', 'c'], [5, 2, 1])─┐
│ [('a',5),('b',2),('c',1)]            │
└──────────────────────────────────────┘

arrayAUC

Calculate AUC (Area Under the Curve, which is a concept in machine learning, see more details: https://en.wikipedia.org/wiki/Receiver_operating_characteristic#Area_under_the_curve).

Syntax

arrayAUC(arr_scores, arr_labels)

Arguments

• arr_scores — scores prediction model gives.
• arr_labels — labels of samples, usually 1 for positive sample and 0 for negtive sample.

Returned value

Returns AUC value with type Float64.

Example

Query:

select arrayAUC([0.1, 0.4, 0.35, 0.8], [0, 0, 1, 1]);

Result:

┌─arrayAUC([0.1, 0.4, 0.35, 0.8], [0, 0, 1, 1])─┐
│                                          0.75 │
└───────────────────────────────────────────────┘

arrayMap(func, arr1, …)

Returns an array obtained from the original arrays by application of func(arr1[i], …, arrN[i]) for each element. Arrays arr1 … arrN must have the same number of elements.

Examples:

SELECT arrayMap(x -> (x + 2), [1, 2, 3]) as res;

┌─res─────┐
│ [3,4,5] │
└─────────┘

The following example shows how to create a tuple of elements from different arrays:

SELECT arrayMap((x, y) -> (x, y), [1, 2, 3], [4, 5, 6]) AS res

┌─res─────────────────┐
│ [(1,4),(2,5),(3,6)] │
└─────────────────────┘

Note that the arrayMap is a higher-order function. You must pass a lambda function to it as the first argument, and it can’t be omitted.

arrayFilter(func, arr1, …)

Returns an array containing only the elements in arr1 for which func(arr1[i], …, arrN[i]) returns something other than 0.

Examples:

SELECT arrayFilter(x -> x LIKE '%World%', ['Hello', 'abc World']) AS res

┌─res───────────┐
│ ['abc World'] │
└───────────────┘

SELECT
    arrayFilter(
        (i, x) -> x LIKE '%World%',
        arrayEnumerate(arr),
        ['Hello', 'abc World'] AS arr)
    AS res

┌─res─┐
│ [2] │
└─────┘

Note that the arrayFilter is a higher-order function. You must pass a lambda function to it as the first argument, and it can’t be omitted.

arrayFill(func, arr1, …)

Scan through arr1 from the first element to the last element and replace arr1[i] by arr1[i - 1] if func(arr1[i], …, arrN[i]) returns 0. The first element of arr1 will not be replaced.

Examples:

SELECT arrayFill(x -> not isNull(x), [1, null, 3, 11, 12, null, null, 5, 6, 14, null, null]) AS res

┌─res──────────────────────────────┐
│ [1,1,3,11,12,12,12,5,6,14,14,14] │
└──────────────────────────────────┘

Note that the arrayFill is a higher-order function. You must pass a lambda function to it as the first argument, and it can’t be omitted.

arrayReverseFill(func, arr1, …)

Scan through arr1 from the last element to the first element and replace arr1[i] by arr1[i + 1] if func(arr1[i], …, arrN[i]) returns 0. The last element of arr1 will not be replaced.

Examples:

SELECT arrayReverseFill(x -> not isNull(x), [1, null, 3, 11, 12, null, null, 5, 6, 14, null, null]) AS res

┌─res────────────────────────────────┐
│ [1,3,3,11,12,5,5,5,6,14,NULL,NULL] │
└────────────────────────────────────┘

Note that the arrayReverseFill is a higher-order function. You must pass a lambda function to it as the first argument, and it can’t be omitted.

arraySplit(func, arr1, …)

Split arr1 into multiple arrays. When func(arr1[i], …, arrN[i]) returns something other than 0, the array will be split on the left hand side of the element. The array will not be split before the first element.

Examples:

SELECT arraySplit((x, y) -> y, [1, 2, 3, 4, 5], [1, 0, 0, 1, 0]) AS res

┌─res─────────────┐
│ [[1,2,3],[4,5]] │
└─────────────────┘

Note that the arraySplit is a higher-order function. You must pass a lambda function to it as the first argument, and it can’t be omitted.

arrayReverseSplit(func, arr1, …)

Split arr1 into multiple arrays. When func(arr1[i], …, arrN[i]) returns something other than 0, the array will be split on the right hand side of the element. The array will not be split after the last element.

Examples:

SELECT arrayReverseSplit((x, y) -> y, [1, 2, 3, 4, 5], [1, 0, 0, 1, 0]) AS res

┌─res───────────────┐
│ [[1],[2,3,4],[5]] │
└───────────────────┘

Note that the arrayReverseSplit is a higher-order function. You must pass a lambda function to it as the first argument, and it can’t be omitted.

arrayExists([func,] arr1, …)

Returns 1 if there is at least one element in arr for which func(arr1[i], …, arrN[i]) returns something other than 0. Otherwise, it returns 0.

Note that the arrayExists is a higher-order function. You can pass a lambda function to it as the first argument.

arrayAll([func,] arr1, …)

Returns 1 if func(arr1[i], …, arrN[i]) returns something other than 0 for all the elements in arrays. Otherwise, it returns 0.

Note that the arrayAll is a higher-order function. You can pass a lambda function to it as the first argument.

arrayFirst(func, arr1, …)

Returns the first element in the arr1 array for which func(arr1[i], …, arrN[i]) returns something other than 0.

Note that the arrayFirst is a higher-order function. You must pass a lambda function to it as the first argument, and it can’t be omitted.

arrayLast(func, arr1, …)

Returns the last element in the arr1 array for which func(arr1[i], …, arrN[i]) returns something other than 0.

Note that the arrayLast is a higher-order function. You must pass a lambda function to it as the first argument, and it can’t be omitted.

arrayFirstIndex(func, arr1, …)

Returns the index of the first element in the arr1 array for which func(arr1[i], …, arrN[i]) returns something other than 0.

Note that the arrayFirstIndex is a higher-order function. You must pass a lambda function to it as the first argument, and it can’t be omitted.

arrayLastIndex(func, arr1, …)

Returns the index of the last element in the arr1 array for which func(arr1[i], …, arrN[i]) returns something other than 0.

Note that the arrayLastIndex is a higher-order function. You must pass a lambda function to it as the first argument, and it can’t be omitted.

arrayMin

Returns the minimum of elements in the source array.

If the func function is specified, returns the mininum of elements converted by this function.

Note that the arrayMin is a higher-order function. You can pass a lambda function to it as the first argument.

Syntax

arrayMin([func,] arr)

Arguments

• func — Function. Expression.
• arr — Array. Array.

Returned value

• The minimum of function values (or the array minimum).

Type: if func is specified, matches func return value type, else matches the array elements type.

Examples

Query:

SELECT arrayMin([1, 2, 4]) AS res;

Result:

┌─res─┐
│   1 │
└─────┘

Query:

SELECT arrayMin(x -> (-x), [1, 2, 4]) AS res;

Result:

┌─res─┐
│  -4 │
└─────┘

arrayMax

Returns the maximum of elements in the source array.

If the func function is specified, returns the maximum of elements converted by this function.

Note that the arrayMax is a higher-order function. You can pass a lambda function to it as the first argument.

Syntax

arrayMax([func,] arr)

Arguments

• func — Function. Expression.
• arr — Array. Array.

Returned value

• The maximum of function values (or the array maximum).

Type: if func is specified, matches func return value type, else matches the array elements type.

Examples

Query:

SELECT arrayMax([1, 2, 4]) AS res;

Result:

┌─res─┐
│   4 │
└─────┘

Query:

SELECT arrayMax(x -> (-x), [1, 2, 4]) AS res;

Result:

┌─res─┐
│  -1 │
└─────┘

arraySum

Returns the sum of elements in the source array.

If the func function is specified, returns the sum of elements converted by this function.

Note that the arraySum is a higher-order function. You can pass a lambda function to it as the first argument.

Syntax

arraySum([func,] arr)

Arguments

• func — Function. Expression.
• arr — Array. Array.

Returned value

• The sum of the function values (or the array sum).

Type: for decimal numbers in source array (or for converted values, if func is specified) — Decimal128, for floating point numbers — Float64, for numeric unsigned — UInt64, and for numeric signed — Int64.

Examples

Query:

SELECT arraySum([2, 3]) AS res;

Result:

┌─res─┐
│   5 │
└─────┘

Query:

SELECT arraySum(x -> x*x, [2, 3]) AS res;

Result:

┌─res─┐
│  13 │
└─────┘

arrayAvg

Returns the average of elements in the source array.

If the func function is specified, returns the average of elements converted by this function.

Note that the arrayAvg is a higher-order function. You can pass a lambda function to it as the first argument.

Syntax

arrayAvg([func,] arr)

Arguments

• func — Function. Expression.
• arr — Array. Array.

Returned value

• The average of function values (or the array average).

Type: Float64.

Examples

Query:

SELECT arrayAvg([1, 2, 4]) AS res;

Result:

┌────────────────res─┐
│ 2.3333333333333335 │
└────────────────────┘

Query:

SELECT arrayAvg(x -> (x * x), [2, 4]) AS res;

Result:

┌─res─┐
│  10 │
└─────┘

arrayCumSum([func,] arr1, …)

Returns an array of the partial (running) sums of the elements in the source array arr1. If func is specified, then the sum is computed from applying func to arr1, arr2, ..., arrN, i.e. func(arr1[i], …, arrN[i]).

Syntax

arrayCumSum(arr)

Arguments

• arr — Array of numeric values.

Returned value

• Returns an array of the partial sums of the elements in the source array.

Type: UInt*, Int*, Float*.

Example:

SELECT arrayCumSum([1, 1, 1, 1]) AS res

┌─res──────────┐
│ [1, 2, 3, 4] │
└──────────────┘

Note that the arrayCumSum is a higher-order function. You can pass a lambda function to it as the first argument.

arrayCumSumNonNegative([func,] arr1, …)

Same as arrayCumSum, returns an array of the partial (running) sums of the elements in the source array. If func is specified, then the sum is computed from applying func to arr1, arr2, ..., arrN, i.e. func(arr1[i], …, arrN[i]). Unlike arrayCumSum, if the current running sum is smaller than 0, it is replaced by 0.

Syntax

arrayCumSumNonNegative(arr)

Arguments

• arr — Array of numeric values.

Returned value

• Returns an array of non-negative partial sums of elements in the source array.

Type: UInt*, Int*, Float*.

SELECT arrayCumSumNonNegative([1, 1, -4, 1]) AS res

┌─res───────┐
│ [1,2,0,1] │
└───────────┘

Note that the arraySumNonNegative is a higher-order function. You can pass a lambda function to it as the first argument.

arrayProduct

Multiplies elements of an array.

Syntax

arrayProduct(arr)

Arguments

• arr — Array of numeric values.

Returned value

• A product of array's elements.

Type: Float64.

Examples

Query:

SELECT arrayProduct([1,2,3,4,5,6]) as res;

Result:

┌─res───┐
│ 720   │
└───────┘

Query:

SELECT arrayProduct([toDecimal64(1,8), toDecimal64(2,8), toDecimal64(3,8)]) as res, toTypeName(res);

Return value type is always Float64. Result:

┌─res─┬─toTypeName(arrayProduct(array(toDecimal64(1, 8), toDecimal64(2, 8), toDecimal64(3, 8))))─┐
│ 6   │ Float64                                                                                  │
└─────┴──────────────────────────────────────────────────────────────────────────────────────────┘

Distance functions

All supported functions are described in distance functions documentation.