PostgreSQL

9.18. Array Functions and Operators
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9.18. Array Functions and Operators

Table 9.51 shows the operators available for array types.

Table 9.51. Array Operators

Operator Description Example Result

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[3,1,3]`	`t`
`<@`	is contained by	`ARRAY[2,2,7] <@ 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}`

=

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[3,1,3]

t

<@

is contained by

ARRAY[2,2,7] <@ 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}

The array ordering operators (<, >=, etc) compare the array contents element-by-element, using the default B-tree comparison function for the element data type, and sort based on the first difference. 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.)

The array containment operators (<@ and @>) consider one array to be contained in another one if each of its elements appears in the other one. Duplicates are not treated specially, thus ARRAY[1] and ARRAY[1,1] are each considered to contain the other.

See Section 8.15 for more details about array operator behavior. See Section 11.2 for more details about which operators support indexed operations.

Table 9.52 shows the functions available for use with array types. See Section 8.15 for more information and examples of the use of these functions.

Table 9.52. Array Functions

Function Return Type Description Example Result

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_ndims(anyarray`)`	`int`	returns the number of dimensions of the array	`array_ndims(ARRAY[[1,2,3], [4,5,6]])`	`2`
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_fill(anyelement, +``+int[]+ [`[.optional]#`, ``+int[]#`])`	`anyarray`	returns an array initialized with supplied value and dimensions, optionally with lower bounds other than 1	`array_fill(7, ARRAY[3], ARRAY[2])`	`[2:4]={7,7,7}`
array_length(anyarray, +``+int)	`int`	returns the length of the requested array dimension	`array_length(array[1,2,3], 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_position(anyarray, +``+anyelement+ [`[.optional]#`, ``+int#`])`	`int`	returns the subscript of the first occurrence of the second argument in the array, starting at the element indicated by the third argument or at the first element (array must be one-dimensional)	`array_position(ARRAY['sun','mon','tue','wed','thu','fri','sat'], 'mon')`	`2`
array_positions(anyarray, +``+anyelement)	`int[]`	returns an array of subscripts of all occurrences of the second argument in the array given as first argument (array must be one-dimensional)	`array_positions(ARRAY['A','A','B','A'], 'A')`	`{1,2,4}`
array_prepend(anyelement, +``+anyarray)	`anyarray`	append an element to the beginning of an array	`array_prepend(1, ARRAY[2,3])`	`{1,2,3}`
array_remove(anyarray, +``+anyelement)	`anyarray`	remove all elements equal to the given value from the array (array must be one-dimensional)	`array_remove(ARRAY[1,2,3,2], 2)`	`{1,3}`
array_replace(anyarray, +``+anyelement, +``+anyelement`)`	`anyarray`	replace each array element equal to the given value with a new value	`array_replace(ARRAY[1,2,5,4], 5, 3)`	`{1,2,3,4}`
array_to_string(anyarray, +``+text+ [`[.optional]#`, ``+text#`])`	`text`	concatenates array elements using supplied delimiter and optional null string	`array_to_string(ARRAY[1, 2, 3, NULL, 5], ',', '*')`	`1,2,3,*,5`
array_upper(anyarray, +``+int)	`int`	returns upper bound of the requested array dimension	`array_upper(ARRAY[1,8,3,7], 1)`	`4`
cardinality(anyarray`)`	`int`	returns the total number of elements in the array, or 0 if the array is empty	`cardinality(ARRAY[[1,2],[3,4]])`	`4`
string_to_array(text, +``+text+ [`[.optional]#`, ``+text#`])`	`text[]`	splits string into array elements using supplied delimiter and optional null string	`string_to_array('xx~^~yy~^~zz', '~^~', 'yy')`	`{xx,NULL,zz}`
unnest(anyarray`)`	`setof anyelement`	expand an array to a set of rows	`unnest(ARRAY[1,2])`	`1 2` (2 rows)
unnest(anyarray, +``+anyarray+ [, …])+	`setof anyelement, anyelement [, ...]`	expand multiple arrays (possibly of different types) to a set of rows. This is only allowed in the FROM clause; see Section 7.2.1.4	`unnest(ARRAY[1,2],ARRAY['foo','bar','baz'])`	`1 foo 2 bar NULL baz` (3 rows)

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_ndims(anyarray`)`

int

returns the number of dimensions of the array

array_ndims(ARRAY[[1,2,3], [4,5,6]])

2

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_fill(anyelement, +``+int[]+ [`[.optional]#`, ``+int[]#])

anyarray

returns an array initialized with supplied value and dimensions, optionally with lower bounds other than 1

array_fill(7, ARRAY[3], ARRAY[2])

[2:4]={7,7,7}

array_length(anyarray, +``+int)

int

returns the length of the requested array dimension

array_length(array[1,2,3], 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_position(anyarray, +``+anyelement+ [`[.optional]#`, ``+int#])

int

returns the subscript of the first occurrence of the second argument in the array, starting at the element indicated by the third argument or at the first element (array must be one-dimensional)

array_position(ARRAY['sun','mon','tue','wed','thu','fri','sat'], 'mon')

2

array_positions(anyarray, +``+anyelement)

int[]

returns an array of subscripts of all occurrences of the second argument in the array given as first argument (array must be one-dimensional)

array_positions(ARRAY['A','A','B','A'], 'A')

{1,2,4}

array_prepend(anyelement, +``+anyarray)

anyarray

append an element to the beginning of an array

array_prepend(1, ARRAY[2,3])

{1,2,3}

array_remove(anyarray, +``+anyelement)

anyarray

remove all elements equal to the given value from the array (array must be one-dimensional)

array_remove(ARRAY[1,2,3,2], 2)

{1,3}

array_replace(anyarray, +``+anyelement, +``+anyelement`)`

anyarray

replace each array element equal to the given value with a new value

array_replace(ARRAY[1,2,5,4], 5, 3)

{1,2,3,4}

array_to_string(anyarray, +``+text+ [`[.optional]#`, ``+text#])

text

concatenates array elements using supplied delimiter and optional null string

array_to_string(ARRAY[1, 2, 3, NULL, 5], ',', '*')

1,2,3,*,5

array_upper(anyarray, +``+int)

int

returns upper bound of the requested array dimension

array_upper(ARRAY[1,8,3,7], 1)

4

cardinality(anyarray`)`

int

returns the total number of elements in the array, or 0 if the array is empty

cardinality(ARRAY[[1,2],[3,4]])

4

string_to_array(text, +``+text+ [`[.optional]#`, ``+text#])

text[]

splits string into array elements using supplied delimiter and optional null string

string_to_array('xx~^~yy~^~zz', '~^~', 'yy')

{xx,NULL,zz}

unnest(anyarray`)`

setof anyelement

expand an array to a set of rows

unnest(ARRAY[1,2])

1
2

(2 rows)

unnest(anyarray, +``+anyarray+ [, …])+

setof anyelement, anyelement [, ...]

expand multiple arrays (possibly of different types) to a set of rows. This is only allowed in the FROM clause; see Section 7.2.1.4

unnest(ARRAY[1,2],ARRAY['foo','bar','baz'])

1    foo
2    bar
NULL baz

(3 rows)

In array_position and array_positions, each array element is compared to the searched value using IS NOT DISTINCT FROM semantics.

In array_position, NULL is returned if the value is not found.

In array_positions, NULL is returned only if the array is NULL; if the value is not found in the array, an empty array is returned instead.

In string_to_array, if the delimiter parameter is NULL, each character in the input string will become a separate element in the resulting array. If the delimiter is an empty string, then the entire input string is returned as a one-element array. Otherwise the input string is split at each occurrence of the delimiter string.

In string_to_array, if the null-string parameter is omitted or NULL, none of the substrings of the input will be replaced by NULL. In array_to_string, if the null-string parameter is omitted or NULL, any null elements in the array are simply skipped and not represented in the output string.

Note

There are two differences in the behavior of string_to_array from pre-9.1 versions of PostgreSQL. First, it will return an empty (zero-element) array rather than NULL when the input string is of zero length. Second, if the delimiter string is NULL, the function splits the input into individual characters, rather than returning NULL as before.

See also Section 9.20 about the aggregate function array_agg for use with arrays.

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