Nested Functions
Version 0.3.3

This section describes functions and operators for examining and manipulating nested values. There are three nested data types: lists, structs, and maps.

List Functions

In the descriptions, l is the three element list [4, 5, 6].

Function Description Example Result
list[index] Bracket notation serves as an alias for list_extract. l[2] 6
list_extract(list, index) Extract the indexth (0-based) value from the list. list_extract(l, 2) 6
list_element(list, index) Alias for list_extract. list_element(l, 2) 6
array_extract(list, index) Alias for list_extract. array_extract(l, 2) 6
list[begin:end] Bracket notation with colon is an alias for list_slice. Missing arguments are interpreted as NULLs. l[1:2] [5, 6]
list_slice(list, begin, end) Extract a sublist using slice conventions. NULLs are interpreted as the bounds of the LIST. Negative values are accepted. list_slice(l, 1, NULL) [5,6]
array_slice(list, begin, end) Alias for list_slice. array_slice(l, 1, NULL) [5,6]
list_value(any, ...) Create a LIST containing the argument values. list_value(4, 5, 6) [4, 5, 6]
list_pack(any, ...) Alias for list_value. list_pack(4, 5, 6) [4, 5, 6]
len(list) Return the length of the list. len([1, 2, 3]) 3
array_length(list) Alias for len. array_length([1, 2, 3]) 3
unnest(list) Unnests a list by one level. Note that this is a special function that alters the cardinality of the result. See the UNNEST page for more details. unnest([1, 2, 3]) 1, 2, 3
list_concat(list1, list2) Concatenates two lists. list_concat([2, 3], [4, 5, 6]) [2, 3, 4, 5, 6]
list_cat(list1, list2) Alias for list_concat. list_cat([2, 3], [4, 5, 6]) [2, 3, 4, 5, 6]
array_concat(list1, list2) Alias for list_concat. array_concat([2, 3], [4, 5, 6]) [2, 3, 4, 5, 6]
array_cat(list1, list2) Alias for list_concat. array_cat([2, 3], [4, 5, 6]) [2, 3, 4, 5, 6]
list_prepend(element, list) Prepends element to list. list_prepend(3, [4, 5, 6]) [3, 4, 5, 6]
array_prepend(element, list) Alias for list_prepend. array_prepend(3, [4, 5, 6]) [3, 4, 5, 6]
list_append(list, element) Appends element to list. list_append([2, 3], 4) [2, 3, 4]
array_append(list, element) Alias for list_append. array_append([2, 3], 4) [2, 3, 4]
list_contains(list, element) Returns true if the list contains the element. list_contains([1, 2, NULL], 1) true
list_has(list, element) Alias for list_contains. list_has([1, 2, NULL], 1) true
array_contains(list, element) Alias for list_contains. array_contains([1, 2, NULL], 1) true
array_has(list, element) Alias for list_contains. array_has([1, 2, NULL], 1) true
list_position(list, element) Returns the index of the element if the list contains the element. list_contains([1, 2, NULL], 2) 2
list_indexof(list, element) Alias for list_position. list_indexof([1, 2, NULL], 2) 2
array_position(list, element) Alias for list_position. array_position([1, 2, NULL], 2) 2
array_indexof(list, element) Alias for list_position. array_indexof([1, 2, NULL], 2) 2
list_aggregate(list, name) Executes the aggregate function name on the elements of list. See the List Aggregates section for more details. list_aggregate([1, 2, NULL], 'min') 1
list_aggr(list, name) Alias for list_aggregate. list_aggr([1, 2, NULL], 'min') 1
array_aggregate(list, name) Alias for list_aggregate. array_aggregate([1, 2, NULL], 'min') 1
array_aggr(list, name) Alias for list_aggregate. array_aggr([1, 2, NULL], 'min') 1

Struct Functions

Function Description Example Result
struct.entry Dot notation serves as an alias for struct_extract. ({'i': 3, 's': 'string'}).s string
struct[entry] Bracket notation serves as an alias for struct_extract. ({'i': 3, 's': 'string'})['s'] string
row(any, ...) Create a STRUCT containing the argument values. If the values are column references, the entry name will be the column name; otherwise it will be the string 'vN' where N is the (1-based) position of the argument. row(i, i % 4, i / 4) {'i': 3, 'v2': 3, 'v3': 0}
struct_extract(struct, 'entry') Extract the named entry from the struct. struct_extract(s, 'i') 4
struct_pack(name := any, ...) Create a STRUCT containing the argument values. The entry name will be the bound variable name. struct_pack(i := 4, s := 'string') {'i': 3, 's': 'string'}

Map Functions

Function Description Example Result
map[entry] Alias for element_at map([100, 5], ['a', 'b'])[100] [a]
element_at(map, key) Return a list containing the value for a given key or an empty list if the key is not contained in the map. The type of the key provided in the second parameter must match the type of the map’s keys else an error is returned. element_at(map([100, 5], [42, 43]),100); [42]
map_extract(map, key) Alias of element_at. Return a list containing the value for a given key or an empty list if the key is not contained in the map. The type of the key provided in the second parameter must match the type of the map’s keys else an error is returned. map_extract(map([100, 5], [42, 43]),100); [42]
cardinality(map) Return the size of the map (or the number of entries in the map). cardinality( map([4, 2], ['a', 'b']) ); 2
map() Returns an empty map. map() {}

Range Functions

The functions range and generate_series create a list of values in the range between start and stop. The start parameter is inclusive. For the range function, the stop parameter is exclusive, while for generate_series, it is inclusive.

Based on the number of arguments, the following variants exist:

  • range(start, stop, step)
  • range(start, stop)
  • range(stop)
  • generate_series(start, stop, step)
  • generate_series(start, stop)
  • generate_series(stop)

The default value of start is 0 and the default value of step is 1.

SELECT range(5);
-- [0, 1, 2, 3, 4]

SELECT range(2, 5);
-- [2, 3, 4]

SELECT range(2, 5, 3);
-- [2]

SELECT generate_series(5);
-- [0, 1, 2, 3, 4, 5]

SELECT generate_series(2, 5);
-- [2, 3, 4, 5]

SELECT generate_series(2, 5, 3);
-- [2, 5]

Date ranges are also supported:

SELECT * FROM range(date '1992-01-01', date '1992-03-01', interval '1' month);

┌─────────────────────┐
│        range        │
├─────────────────────┤
│ 1992-01-01 00:00:00 │
│ 1992-02-01 00:00:00 │
└─────────────────────┘

List Aggregates

The function list_aggregate allows the execution of arbitrary existing aggregate functions on the elements of a list. Its first argument is the list (column), its second argument is the aggregate function name, e.g. min, histogram or sum.

SELECT list_aggregate([1, 2, -4, NULL], 'min');
-- -4

SELECT list_aggregate([2, 4, 8, 42], 'sum');
-- 56

SELECT list_aggregate([[1, 2], [NULL], [2, 10, 3]], 'last');
-- [2, 10, 3]

The following is a list of existing rewrites. Rewrites simplify the use of the list aggregate function by only taking the list (column) as their argument. list_avg, list_var_samp, list_var_pop, list_stddev_pop, list_stddev_samp, list_sem, list_approx_count_distinct, list_bit_xor, list_bit_or, list_bit_and, list_bool_and, list_bool_or, list_count, list_entropy, list_last, list_first, list_kurtosis, list_min, list_max, list_product, list_skewness, list_sum, list_string_agg, list_mode, list_median, list_mad and list_histogram.

SELECT list_min([1, 2, -4, NULL]);
-- -4

SELECT list_sum([2, 4, 8, 42]);
-- 56

SELECT list_last([[1, 2], [NULL], [2, 10, 3]]);
-- [2, 10, 3]

generate_subscripts

The generate_subscript(arr, dim) function generates indexes along the dimth dimension of array arr.

SELECT generate_subscripts([4,5,6], 1) AS i;
┌───┐
│ i │
├───┤
│ 1 │
│ 2 │
│ 3 │
└───┘

There are also aggregate functions list and histogram that produces lists and lists of structs.