9.18. Array Functions and Operators

Table 9-47 shows the operators available for array types.

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 9-48 shows the functions available for use with array types. See Section 8.15 for more information and examples of the use of these functions.

1
2

1    foo
2    bar
NULL baz

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.