7.16. Array Functions and Operators

Subscript Operator: []

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

  1. 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:

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

Array Functions

  • all_match(array(T), function(T, boolean)) → boolean
  • Returns whether all elements of an array match the given predicate. Returns true if all the elementsmatch the predicate (a special case is when the array is empty); false if one or more elements don’tmatch; NULL if the predicate function returns NULL for one or more elements and true for allother elements.
  • any_match(array(T), function(T, boolean)) → boolean
  • Returns whether any elements of an array match the given predicate. Returns true if one or moreelements match the predicate; false if none of the elements matches (a special case is when thearray is empty); NULL if the predicate function returns NULL for one or more elements and falsefor all other elements.
  • array_distinct(x) → array
  • Remove duplicate values from the array x.
  • array_except(x, y) → array
  • Returns an array of elements in x but not in y, without duplicates.
  • array_intersect(x, y) → array
  • Returns an array of the elements in the intersection of x and y, without duplicates.
  • array_join(x, delimiter, null_replacement) → varchar
  • Concatenates the elements of the given array using the delimiter and an optional string to replace nulls.
  • array_max(x) → x
  • Returns the maximum value of input array.
  • array_min(x) → x
  • Returns the minimum value of input array.
  • array_position(x, element) → bigint
  • Returns the position of the first occurrence of the element in array x (or 0 if not found).
  • array_remove(x, element) → array
  • Remove all elements that equal element from array x.
  • array_sort(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.
  • array_sort(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 
    1. SELECT array_sort(ARRAY [3, 2, 5, 1, 2], (x, y) -> IF(x < y, 1, IF(x = y, 0, -1))); — [5, 3, 2, 2, 1]
    2. SELECT array_sort(ARRAY ['bc', 'ab', 'dc'], (x, y) -> IF(x < y, 1, IF(x = y, 0, -1))); — ['dc', 'bc', 'ab']
    3. SELECT array_sort(ARRAY [3, 2, null, 5, null, 1, 2], — sort null first with descending order
    4.                   (x, y) -> CASE WHEN x IS NULL THEN -1
    5.                                  WHEN y IS NULL THEN 1
    6.                                  WHEN x < y THEN 1
    7.                                  WHEN x = y THEN 0
    8.                                  ELSE -1 END); — [null, null, 5, 3, 2, 2, 1]
    9. SELECT array_sort(ARRAY [3, 2, null, 5, null, 1, 2], — sort null last with descending order
    10.                   (x, y) -> CASE WHEN x IS NULL THEN 1
    11.                                  WHEN y IS NULL THEN -1
    12.                                  WHEN x < y THEN 1
    13.                                  WHEN x = y THEN 0
    14.                                  ELSE -1 END); — [5, 3, 2, 2, 1, null, null]
    15. SELECT array_sort(ARRAY ['a', 'abcd', 'abc'], — sort by string length
    16.                   (x, y) -> IF(length(x) < length(y),
    17.                                -1,
    18.                                IF(length(x) = length(y), 0, 1))); — ['a', 'abc', 'abcd']
    19. SELECT array_sort(ARRAY [ARRAY[2, 3, 1], ARRAY[4, 2, 1, 4], ARRAY[1, 2]], — sort by array length
    20.                   (x, y) -> IF(cardinality(x) < cardinality(y),
    21.                                -1,
    22.                                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 non-null elements in common.Returns null if there are no non-null elements in common but either array contains null.
  • array_union(x, y) → array
  • Returns an array of the elements in the union of x and y, without duplicates.
  • 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 (||).
  • combinations(array(T), n) -> array(array(T))
  • Returns n-element combinations of the input array.If the input array has no duplicates, combinations returns n-element subsets.Order of subgroup is deterministic but unspecified. Order of elements withina subgroup are deterministic but unspecified. n must not be greater than 5,and the total size of subgroups generated must be smaller than 100000: 
    1. SELECT combinations(ARRAY['foo', 'bar', 'boo'],2); —[['foo', 'bar'], ['foo', 'boo']['bar', 'boo']]
    2. SELECT combinations(ARRAY[1,2,3,4,5],3); —[[1,2,3], [1,2,4], [1,3,4], [2,3,4]]
    3. SELECT combinations(ARRAY[1,2,2],2); —[[1,2],[1,2],[2,2]]
  • contains(x, element) → boolean
  • Returns true if the array x contains the element.
  • element_at(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, element_at 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: 
    1. SELECT filter(ARRAY [], x -> true); — []
    2. SELECT filter(ARRAY [5, -6, NULL, 7], x -> x > 0); — [5, 7]
    3. 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.
  • ngrams(array(T), n) -> array(array(T))
  • Returns n-grams for the array: 
    1. SELECT ngrams(ARRAY['foo', 'bar', 'baz', 'foo'], 2); — [['foo', 'bar'], ['bar', 'baz'], ['baz', 'foo']]
    2. SELECT ngrams(ARRAY['foo', 'bar', 'baz', 'foo'], 3); — [['foo', 'bar', 'baz'], ['bar', 'baz', 'foo']]
    3. SELECT ngrams(ARRAY['foo', 'bar', 'baz', 'foo'], 4); — [['foo', 'bar', 'baz', 'foo']]
    4. SELECT ngrams(ARRAY['foo', 'bar', 'baz', 'foo'], 5); — [['foo', 'bar', 'baz', 'foo']]
    5. SELECT ngrams(ARRAY[1, 2, 3, 4], 2); — [[1, 2], [2, 3], [3, 4]]
  • none_match(array(T), function(T, boolean)) → boolean
  • Returns whether no elements of an array match the given predicate. Returns true if none of the elementsmatches the predicate (a special case is when the array is empty); false if one or more elements match;NULL if the predicate function returns NULL for one or more elements and false for all other elements.
  • 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). 
    1. SELECT reduce(ARRAY [], 0, (s, x) -> s + x, s -> s); — 0
    2. SELECT reduce(ARRAY [5, 20, 50], 0, (s, x) -> s + x, s -> s); — 75
    3. SELECT reduce(ARRAY [5, 20, NULL, 50], 0, (s, x) -> s + x, s -> s); — NULL
    4. SELECT reduce(ARRAY [5, 20, NULL, 50], 0, (s, x) -> s + COALESCE(x, 0), s -> s); — 75
    5. SELECT reduce(ARRAY [5, 20, NULL, 50], 0, (s, x) -> IF(x IS NULL, s, s + x), s -> s); — 75
    6. SELECT reduce(ARRAY [2147483647, 1], CAST (0 AS BIGINT), (s, x) -> s + x, s -> s); — 2147483648
    7. SELECT reduce(ARRAY [5, 6, 10, 20], — calculates arithmetic average: 10.25
    8.               CAST(ROW(0.0, 0) AS ROW(sum DOUBLE, count INTEGER)),
    9.               (s, x) -> CAST(ROW(x + s.sum, s.count + 1) AS ROW(sum DOUBLE, count INTEGER)),
    10.               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: 
    1. SELECT transform(ARRAY [], x -> x + 1); — []
    2. SELECT transform(ARRAY [5, 6], x -> x + 1); — [6, 7]
    3. SELECT transform(ARRAY [5, NULL, 6], x -> COALESCE(x, 0) + 1); — [6, 1, 7]
    4. SELECT transform(ARRAY ['x', 'abc', 'z'], x -> x || '0'); — ['x0', 'abc0', 'z0']
    5. 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. 
    1. SELECT zip(ARRAY[1, 2], ARRAY['1b', null, '3b']); — [ROW(1, '1b'), ROW(2, null), ROW(null, '3b')]
  • zip_with(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: 
    1. SELECT zip_with(ARRAY[1, 3, 5], ARRAY['a', 'b', 'c'], (x, y) -> (y, x)); — [ROW('a', 1), ROW('b', 3), ROW('c', 5)]
    2. SELECT zip_with(ARRAY[1, 2], ARRAY[3, 4], (x, y) -> x + y); — [4, 6]
    3. SELECT zip_with(ARRAY['a', 'b', 'c'], ARRAY['d', 'e', 'f'], (x, y) -> concat(x, y)); — ['ad', 'be', 'cf']
    4. SELECT zip_with(ARRAY['a'], ARRAY['d', null, 'f'], (x, y) -> coalesce(x, y)); — ['a', null, 'f']