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.

Table 9.51. Array Operators

Operator Description Example(s)
anyarray @> anyarray → boolean 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 <@ anyarray → boolean Is the first array contained by the second? ARRAY[2,2,7] <@ ARRAY[1,7,4,2,6] → t
anyarray && anyarray → boolean Do the arrays overlap, that is, have any elements in common? ARRAY[1,4,3] && ARRAY[2,1] → t
anycompatiblearray || anycompatiblearray → anycompatiblearray 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). If the arrays are not of identical element types, they will be coerced to a common type (see Section 10.5). ARRAY[1,2,3] || ARRAY[4,5,6,7] → {1,2,3,4,5,6,7} ARRAY[1,2,3] || ARRAY[[4,5,6],[7,8,9.9]] → {{1,2,3},{4,5,6},{7,8,9.9}}
anycompatible || anycompatiblearray → anycompatiblearray 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}
anycompatiblearray || anycompatible → anycompatiblearray 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 ( anycompatiblearray, anycompatible ) → anycompatiblearray Appends an element to the end of an array (same as the anycompatiblearray || anycompatible operator). array_append(ARRAY[1,2], 3) → {1,2,3}
array_cat ( anycompatiblearray, anycompatiblearray ) → anycompatiblearray Concatenates two arrays (same as the anycompatiblearray || anycompatiblearray 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 ( anycompatiblearray, anycompatible [, 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 ( anycompatiblearray, anycompatible ) → 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 ( anycompatible, anycompatiblearray ) → anycompatiblearray Prepends an element to the beginning of an array (same as the anycompatible || anycompatiblearray operator). array_prepend(1, ARRAY[2,3]) → {1,2,3}
array_remove ( anycompatiblearray, anycompatible ) → anycompatiblearray 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 ( anycompatiblearray, anycompatible, anycompatible ) → anycompatiblearray 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
trim_array ( array anyarray, n integer ) → anyarray Trims an array by removing the last n elements. If the array is multidimensional, only the first dimension is trimmed. trim_array(ARRAY[1,2,3,4,5,6], 2) → {1,2,3,4}
unnest ( anyarray ) → setof anyelement Expands an array into a set of rows. The array's elements are read out in storage order. unnest(ARRAY[1,2]) → <br/><br/>```<br/> 1<br/> 2<br/><br/>```<br/><br/>`unnest(ARRAY[['foo','bar'],['baz','quux']])` → <br/> foo<br/> bar<br/> baz<br/> quux<br/><br/>
unnest ( anyarray, anyarray [, ... ] ) → setof anyelement, anyelement [, ... ] Expands multiple arrays (possibly of different data types) into a set of rows. If the arrays are not all the same length then the shorter ones are padded with NULLs. This form 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) → `` <br/> a | b<br/>---+-----<br/> 1 | foo<br/> 2 | bar<br/> | baz<br/><br/>

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.