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9.17. Array Functions and Operators

Table 9-39 shows the operators available for array types.

Table 9-39. array Operators

Operator Description Example Result
= equal ARRAY[1.1,2.1,3.1]::int[] = ARRAY[1,2,3] t
<> not equal ARRAY[1,2,3] <> ARRAY[1,2,4] t
< less than ARRAY[1,2,3] < ARRAY[1,2,4] t
> greater than ARRAY[1,4,3] > ARRAY[1,2,4] t
<= less than or equal ARRAY[1,2,3] <= ARRAY[1,2,3] t
>= greater than or equal ARRAY[1,4,3] >= ARRAY[1,4,3] t
@> contains ARRAY[1,4,3] @> ARRAY[3,1] t
<@ is contained by ARRAY[2,7] <@ ARRAY[1,7,4,2,6] t
&& overlap (have elements in common) ARRAY[1,4,3] && ARRAY[2,1] t
|| array-to-array concatenation ARRAY[1,2,3] || ARRAY[4,5,6] {1,2,3,4,5,6}
|| array-to-array concatenation ARRAY[1,2,3] || ARRAY[[4,5,6],[7,8,9]] {{1,2,3},{4,5,6},{7,8,9}}
|| element-to-array concatenation 3 || ARRAY[4,5,6] {3,4,5,6}
|| array-to-element concatenation ARRAY[4,5,6] || 7 {4,5,6,7}

Array comparisons compare the array contents element-by-element, using the default B-Tree comparison function for the element data type. In multidimensional arrays the elements are visited in row-major order (last subscript varies most rapidly). If the contents of two arrays are equal but the dimensionality is different, the first difference in the dimensionality information determines the sort order. (This is a change from versions of PostgreSQL prior to 8.2: older versions would claim that two arrays with the same contents were equal, even if the number of dimensions or subscript ranges were different.)

See Section 8.14 for more details about array operator behavior.

Table 9-40 shows the functions available for use with array types. See Section 8.14 for more discussion and examples of the use of these functions.

Table 9-40. array Functions

Function Return Type Description Example Result
array_append(anyarray, anyelement) anyarray append an element to the end of an array array_append(ARRAY[1,2], 3) {1,2,3}
array_cat(anyarray, anyarray) anyarray concatenate two arrays array_cat(ARRAY[1,2,3], ARRAY[4,5]) {1,2,3,4,5}
array_dims(anyarray) text returns a text representation of array's dimensions array_dims(ARRAY[[1,2,3], [4,5,6]]) [1:2][1:3]
array_lower(anyarray, int) int returns lower bound of the requested array dimension array_lower('[0:2]={1,2,3}'::int[], 1) 0
array_prepend(anyelement, anyarray) anyarray append an element to the beginning of an array array_prepend(1, ARRAY[2,3]) {1,2,3}
array_to_string(anyarray, text) text concatenates array elements using provided delimiter array_to_string(ARRAY[1, 2, 3], '~^~') 1~^~2~^~3
array_upper(anyarray, int) int returns upper bound of the requested array dimension array_upper(ARRAY[1,2,3,4], 1) 4
string_to_array(text, text) text[] splits string into array elements using provided delimiter string_to_array('xx~^~yy~^~zz', '~^~') {xx,yy,zz}


April 8, 2009, 4:28 p.m.

When given an empty-string as input, as in array_to_string('',','), the result is null. Users desiring a non-null result must test for an empty-string and generate their desired output. There exists the possibility that this function may be altered to return either an empty array or an array with a single empty-string element in some future release.

April 8, 2009, 9:35 p.m.

Following PLPGSQL function can be used to find an element's position in an array:

create or replace function find_array_element( el anyelement, arr anyarray ) returns integer as $$
i int;
for i in 1..array_upper( arr, 1 ) loop
if( el = arr[i] ) then
return i;
end if;
end loop;
return 0;
$$ language plpgsql;

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