Table 9-41 shows the operators
available for array types.
Table 9-41. 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 9-42 shows the functions
available for use with array types. See Section 8.14
for more information and examples of the use of these functions.
Table 9-42. 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_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[],
[, 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_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])
text
concatenates array elements using supplied delimiter and
optional null string
returns upper bound of the requested array dimension
array_upper(ARRAY[1,8,3,7], 1)
4
string_to_array(text, text [, 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)
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 9.18 about the aggregate
function array_agg for use with arrays.