Table 9.51 shows the operators available for array types.
Table 9.51. 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[3,1,3] 
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 
 
arraytoarray concatenation  ARRAY[1,2,3]  ARRAY[4,5,6] 
{1,2,3,4,5,6} 
 
arraytoarray concatenation  ARRAY[1,2,3]  ARRAY[[4,5,6],[7,8,9]] 
{{1,2,3},{4,5,6},{7,8,9}} 
 
elementtoarray concatenation  3  ARRAY[4,5,6] 
{3,4,5,6} 
 
arraytoelement concatenation  ARRAY[4,5,6]  7 
{4,5,6,7} 
The array ordering operators (<
, >=
, etc) compare the array contents elementbyelement, using the default Btree comparison function for the element data type, and sort based on the first difference. In multidimensional arrays the elements are visited in rowmajor 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 


anyarray 
append an element to the end of an array  array_append(ARRAY[1,2], 3) 
{1,2,3} 

anyarray 
concatenate two arrays  array_cat(ARRAY[1,2,3], ARRAY[4,5]) 
{1,2,3,4,5} 

int 
returns the number of dimensions of the array  array_ndims(ARRAY[[1,2,3], [4,5,6]]) 
2 

text 
returns a text representation of array's dimensions  array_dims(ARRAY[[1,2,3], [4,5,6]]) 
[1:2][1:3] 

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} 

int 
returns the length of the requested array dimension  array_length(array[1,2,3], 1) 
3 

int 
returns lower bound of the requested array dimension  array_lower('[0:2]={1,2,3}'::int[], 1) 
0 

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 onedimensional)  array_position(ARRAY['sun','mon','tue','wed','thu','fri','sat'], 'mon') 
2 

int[] 
returns an array of subscripts of all occurrences of the second argument in the array given as first argument (array must be onedimensional)  array_positions(ARRAY['A','A','B','A'], 'A') 
{1,2,4} 

anyarray 
append an element to the beginning of an array  array_prepend(1, ARRAY[2,3]) 
{1,2,3} 

anyarray 
remove all elements equal to the given value from the array (array must be onedimensional)  array_remove(ARRAY[1,2,3,2], 2) 
{1,3} 

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} 

text 
concatenates array elements using supplied delimiter and optional null string  array_to_string(ARRAY[1, 2, 3, NULL, 5], ',', '*') 
1,2,3,*,5 

int 
returns upper bound of the requested array dimension  array_upper(ARRAY[1,8,3,7], 1) 
4 

int 
returns the total number of elements in the array, or 0 if the array is empty  cardinality(ARRAY[[1,2],[3,4]]) 
4 

text[] 
splits string into array elements using supplied delimiter and optional null string  string_to_array('xx~^~yy~^~zz', '~^~', 'yy') 
{xx,NULL,zz} 

setof anyelement 
expand an array to a set of rows  unnest(ARRAY[1,2]) 
1 2(2 rows) 

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 oneelement array. Otherwise the input string is split at each occurrence of the delimiter string.
In string_to_array
, if the nullstring parameter is omitted or NULL, none of the substrings of the input will be replaced by NULL. In array_to_string
, if the nullstring parameter is omitted or NULL, any null elements in the array are simply skipped and not represented in the output string.
There are two differences in the behavior of string_to_array
from pre9.1 versions of PostgreSQL. First, it will return an empty (zeroelement) 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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