6.16. Array Functions and Operators

6.16. Array Functions and Operators

Subscript Operator: []

The [] operator is used to access an element of an array and is indexed starting from one:

SELECT my_array[1] AS first_element

Concatenation Operator: ||

The || operator is used to concatenate an array with an array or an element of the same type:

SELECT ARRAY [1] || ARRAY [2]; -- [1, 2]
SELECT ARRAY [1] || 2; -- [1, 2]
SELECT 2 || ARRAY [1]; -- [2, 1]

Array Functions

arraydistinct(_x) → array: Remove duplicate values from the array x.

arrayintersect(_x, y) → array: Returns an array of the elements in the intersection of x and y, without duplicates.

arrayunion(_x, y) → array: Returns an array of the elements in the union of x and y, without duplicates.

arrayexcept(_x, y) → array: Returns an array of elements in x but not in y, without duplicates.

arrayjoin(_x, delimiter, null_replacement) → varchar: Concatenates the elements of the given array using the delimiter and an optional string to replace nulls.

arraymax(_x) → x: Returns the maximum value of input array.

arraymin(_x) → x: Returns the minimum value of input array.

arrayposition(_x, element) → bigint: Returns the position of the first occurrence of the element in array x (or 0 if not found).

arrayremove(_x, element) → array: Remove all elements that equal element from array x.

arraysort(_x) → array: Sorts and returns the array x. The elements of x must be orderable.Null elements will be placed at the end of the returned array.

arraysort(_array<T>, function<T, T, int>) → array<T>

Sorts and returns the array based on the given comparator function. The comparator will taketwo nullable arguments representing two nullable elements of the array. It returns -1, 0, or 1as the first nullable element is less than, equal to, or greater than the second nullable element.If the comparator function returns other values (including NULL), the query will fail and raise an error

SELECT arraysort(ARRAY [3, 2, 5, 1, 2], (x, y) -> IF(x < y, 1, IF(x = y, 0, -1))); — [5, 3, 2, 2, 1]
SELECT array_sort(ARRAY ['bc', 'ab', 'dc'], (x, y) -> IF(x < y, 1, IF(x = y, 0, -1))); — ['dc', 'bc', 'ab']
SELECT array_sort(ARRAY [3, 2, null, 5, null, 1, 2], — sort null first with descending order
                  (x, y) -> CASE WHEN x IS NULL THEN -1
                                 WHEN y IS NULL THEN 1
                                 WHEN x < y THEN 1
                                 WHEN x = y THEN 0
                                 ELSE -1 END); — [null, null, 5, 3, 2, 2, 1]
SELECT array_sort(ARRAY [3, 2, null, 5, null, 1, 2], — sort null last with descending order
                  (x, y) -> CASE WHEN x IS NULL THEN 1
                                 WHEN y IS NULL THEN -1
                                 WHEN x < y THEN 1
                                 WHEN x = y THEN 0
                                 ELSE -1 END); — [5, 3, 2, 2, 1, null, null]
SELECT array_sort(ARRAY ['a', 'abcd', 'abc'], — sort by string length
                  (x, y) -> IF(length(x) < length(y),
                               -1,
                               IF(length(x) = length(y), 0, 1))); — ['a', 'abc', 'abcd']
SELECT array_sort(ARRAY [ARRAY[2, 3, 1], ARRAY[4, 2, 1, 4], ARRAY[1, 2]], — sort by array length
                  (x, y) -> IF(cardinality(x) < cardinality(y),
                               -1,
                               IF(cardinality(x) = cardinality(y), 0, 1))); — [[1, 2], [2, 3, 1], [4, 2, 1, 4]]

arrays_overlap(_x, y) → boolean: Tests if arrays x and y have any any non-null elements in common.Returns null if there are no non-null elements in common but either array contains null.

cardinality(x) → bigint: Returns the cardinality (size) of the array x.

concat(array1, array2, …, arrayN) → array: Concatenates the arrays array1, array2, …, arrayN.This function provides the same functionality as the SQL-standard concatenation operator (||).

contains(x, element) → boolean: Returns true if the array x contains the element.

elementat(_array<E>, index) → E: Returns element of array at given index.If index > 0, this function provides the same functionality as the SQL-standard subscript operator ([]).If index < 0, elementat accesses elements from the last to the first.

filter(_array<T>, function<T, boolean>) → array<T>

Constructs an array from those elements of array for which function returns true:

SELECT filter(ARRAY [], x -> true); — []
SELECT filter(ARRAY [5, -6, NULL, 7], x -> x > 0); — [5, 7]
SELECT filter(ARRAY [5, NULL, 7, NULL], x -> x IS NOT NULL); — [5, 7]

flatten(x) → array: Flattens an array(array(T)) to an array(T) by concatenating the contained arrays.

reduce(array<T>, initialState S, inputFunction<S, T, S>, outputFunction<S, R>) → R

Returns a single value reduced from array. inputFunction willbe invoked for each element in array in order. In addition to takingthe element, inputFunction takes the current state, initiallyinitialState, and returns the new state. outputFunction will beinvoked to turn the final state into the result value. It may be theidentity function (i -> i).

SELECT reduce(ARRAY [], 0, (s, x) -> s + x, s -> s); — 0
SELECT reduce(ARRAY [5, 20, 50], 0, (s, x) -> s + x, s -> s); — 75
SELECT reduce(ARRAY [5, 20, NULL, 50], 0, (s, x) -> s + x, s -> s); — NULL
SELECT reduce(ARRAY [5, 20, NULL, 50], 0, (s, x) -> s + COALESCE(x, 0), s -> s); — 75
SELECT reduce(ARRAY [5, 20, NULL, 50], 0, (s, x) -> IF(x IS NULL, s, s + x), s -> s); — 75
SELECT reduce(ARRAY [2147483647, 1], CAST (0 AS BIGINT), (s, x) -> s + x, s -> s); — 2147483648
SELECT reduce(ARRAY [5, 6, 10, 20], — calculates arithmetic average: 10.25
              CAST(ROW(0.0, 0) AS ROW(sum DOUBLE, count INTEGER)),
              (s, x) -> CAST(ROW(x + s.sum, s.count + 1) AS ROW(sum DOUBLE, count INTEGER)),
              s -> IF(s.count = 0, NULL, s.sum / s.count));

repeat(element, count) → array: Repeat element for count times.

reverse(x) → array: Returns an array which has the reversed order of array x.

sequence(start, stop) → array<bigint>: Generate a sequence of integers from start to stop, incrementingby 1 if start is less than or equal to stop, otherwise -1.

sequence(start, stop, step) → array<bigint>: Generate a sequence of integers from start to stop, incrementing by step.

sequence(start, stop) → array<date>: Generate a sequence of dates from start date to stop date, incrementingby 1 day if start date is less than or equal to stop date, otherwise -1 day.

sequence(start, stop, step) → array<date>: Generate a sequence of dates from start to stop, incrementing by step.The type of step can be either INTERVAL DAY TO SECOND or INTERVAL YEAR TO MONTH.

sequence(start, stop, step) → array<timestamp>: Generate a sequence of timestamps from start to stop, incrementing by step.The type of step can be either INTERVAL DAY TO SECOND or INTERVAL YEAR TO MONTH.

shuffle(x) → array: Generate a random permutation of the given array x.

slice(x, start, length) → array: Subsets array x starting from index start (or starting from the endif start is negative) with a length of length.

transform(array<T>, function<T, U>) → array<U>

Returns an array that is the result of applying function to each element of array:

SELECT transform(ARRAY [], x -> x + 1); — []
SELECT transform(ARRAY [5, 6], x -> x + 1); — [6, 7]
SELECT transform(ARRAY [5, NULL, 6], x -> COALESCE(x, 0) + 1); — [6, 1, 7]
SELECT transform(ARRAY ['x', 'abc', 'z'], x -> x || '0'); — ['x0', 'abc0', 'z0']
SELECT transform(ARRAY [ARRAY [1, NULL, 2], ARRAY[3, NULL]], a -> filter(a, x -> x IS NOT NULL)); — [[1, 2], [3]]

zip(array1, array2[, …]) → array<row>

Merges the given arrays, element-wise, into a single array of rows. The M-th element ofthe N-th argument will be the N-th field of the M-th output element.If the arguments have an uneven length, missing values are filled with NULL.

SELECT zip(ARRAY[1, 2], ARRAY['1b', null, '3b']); — [ROW(1, '1b'), ROW(2, null), ROW(null, '3b')]

zipwith(_array<T>, array<U>, function<T, U, R>) → array<R>

Merges the two given arrays, element-wise, into a single array using function.If one array is shorter, nulls are appended at the end to match the length of the longer array, before applying function:

SELECT zip_with(ARRAY[1, 3, 5], ARRAY['a', 'b', 'c'], (x, y) -> (y, x)); — [ROW('a', 1), ROW('b', 3), ROW('c', 5)]
SELECT zip_with(ARRAY[1, 2], ARRAY[3, 4], (x, y) -> x + y); — [4, 6]
SELECT zip_with(ARRAY['a', 'b', 'c'], ARRAY['d', 'e', 'f'], (x, y) -> concat(x, y)); — ['ad', 'be', 'cf']
SELECT zip_with(ARRAY['a'], ARRAY['d', null, 'f'], (x, y) -> coalesce(x, y)); — ['a', null, 'f']

原文: https://prestodb.io/docs/current/functions/array.html