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9.19. Array Functions and Operators

Table 9.51 shows the specialized operators available for array types. In addition to those, the usual comparison operators shown in Table 9.1 are available for arrays. The comparison operators 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.)

Table 9.51. Array Operators

Operator

Description

Example(s)

anyarray @> anyarrayboolean

Does the first array contain the second, that is, does each element appearing in the second array equal some element of the first array? (Duplicates are not treated specially, thus ARRAY[1] and ARRAY[1,1] are each considered to contain the other.)

ARRAY[1,4,3] @> ARRAY[3,1,3]t

anyarray <@ anyarrayboolean

Is the first array contained by the second?

ARRAY[2,2,7] <@ ARRAY[1,7,4,2,6]t

anyarray && anyarrayboolean

Do the arrays overlap, that is, have any elements in common?

ARRAY[1,4,3] && ARRAY[2,1]t

anyarray || anyarrayanyarray

Concatenates the two arrays. Concatenating a null or empty array is a no-op; otherwise the arrays must have the same number of dimensions (as illustrated by the first example) or differ in number of dimensions by one (as illustrated by the second).

ARRAY[1,2,3] || ARRAY[4,5,6,7]{1,2,3,4,5,6,7}

ARRAY[1,2,3] || ARRAY[[4,5,6],[7,8,9]]{{1,2,3},{4,5,6},{7,8,9}}

anyelement || anyarrayanyarray

Concatenates an element onto the front of an array (which must be empty or one-dimensional).

3 || ARRAY[4,5,6]{3,4,5,6}

anyarray || anyelementanyarray

Concatenates an element onto the end of an array (which must be empty or one-dimensional).

ARRAY[4,5,6] || 7{4,5,6,7}


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

Description

Example(s)

array_append ( anyarray, anyelement ) → anyarray

Appends an element to the end of an array (same as the anyarray || anyelement operator).

array_append(ARRAY[1,2], 3){1,2,3}

array_cat ( anyarray, anyarray ) → anyarray

Concatenates two arrays (same as the anyarray || anyarray operator).

array_cat(ARRAY[1,2,3], ARRAY[4,5]){1,2,3,4,5}

array_dims ( anyarray ) → text

Returns a text representation of the array's dimensions.

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

array_fill ( anyelement, integer[] [, integer[] ] ) → anyarray

Returns an array filled with copies of the given value, having dimensions of the lengths specified by the second argument. The optional third argument supplies lower-bound values for each dimension (which default to all 1).

array_fill(11, ARRAY[2,3]){{11,11,11},{11,11,11}}

array_fill(7, ARRAY[3], ARRAY[2])[2:4]={7,7,7}

array_length ( anyarray, integer ) → integer

Returns the length of the requested array dimension.

array_length(array[1,2,3], 1)3

array_lower ( anyarray, integer ) → integer

Returns the lower bound of the requested array dimension.

array_lower('[0:2]={1,2,3}'::integer[], 1)0

array_ndims ( anyarray ) → integer

Returns the number of dimensions of the array.

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

array_position ( anyarray, anyelement [, integer ] ) → integer

Returns the subscript of the first occurrence of the second argument in the array, or NULL if it's not present. If the third argument is given, the search begins at that subscript. The array must be one-dimensional. Comparisons are done using IS NOT DISTINCT FROM semantics, so it is possible to search for NULL.

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

array_positions ( anyarray, anyelement ) → integer[]

Returns an array of the subscripts of all occurrences of the second argument in the array given as first argument. The array must be one-dimensional. Comparisons are done using IS NOT DISTINCT FROM semantics, so it is possible to search for NULL. NULL is returned only if the array is NULL; if the value is not found in the array, an empty array is returned.

array_positions(ARRAY['A','A','B','A'], 'A'){1,2,4}

array_prepend ( anyelement, anyarray ) → anyarray

Prepends an element to the beginning of an array (same as the anyelement || anyarray operator).

array_prepend(1, ARRAY[2,3]){1,2,3}

array_remove ( anyarray, anyelement ) → anyarray

Removes all elements equal to the given value from the array. The array must be one-dimensional. Comparisons are done using IS NOT DISTINCT FROM semantics, so it is possible to remove NULLs.

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

array_replace ( anyarray, anyelement, anyelement ) → anyarray

Replaces each array element equal to the second argument with the third argument.

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

array_to_string ( array anyarray, delimiter text [, null_string text ] ) → text

Converts each array element to its text representation, and concatenates those separated by the delimiter string. If null_string is given and is not NULL, then NULL array entries are represented by that string; otherwise, they are omitted.

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

array_upper ( anyarray, integer ) → integer

Returns the upper bound of the requested array dimension.

array_upper(ARRAY[1,8,3,7], 1)4

cardinality ( anyarray ) → integer

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 ( string text, delimiter text [, null_string text ] ) → text[]

Splits the string at occurrences of delimiter and forms the remaining data into a text array. If delimiter is NULL, each character in the string will become a separate element in the array. If delimiter is an empty string, then the string is treated as a single field. If null_string is supplied and is not NULL, fields matching that string are converted to NULL entries.

string_to_array('xx~~yy~~zz', '~~', 'yy'){xx,NULL,zz}

unnest ( anyarray ) → setof anyelement

Expands an array to a set of rows.

unnest(ARRAY[1,2])

 1
 2

unnest ( anyarray, anyarray [, ... ] ) → setof anyelement, anyelement [, ... ]

Expands multiple arrays (possibly of different data types) to a set of rows. If the arrays are not all the same length then the shorter ones are padded with NULLs. This is only allowed in a query's FROM clause; see Section 7.2.1.4.

select * from unnest(ARRAY[1,2], ARRAY['foo','bar','baz']) as x(a,b)

 a |  b
---+-----
 1 | foo
 2 | bar
   | baz

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 9.21 about the aggregate function array_agg for use with arrays.