9.18. 陣列函式及運算子

Table 9.48shows the operators available for array types.

Table 9.48. 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 ofPostgreSQLprior 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.)

SeeSection 8.15for more details about array operator behavior. SeeSection 11.2for more details about which operators support indexed operations.

Table 9.49shows the functions available for use with array types. SeeSection 8.15for more information and examples of the use of these functions.

Table 9.49. 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_position(anyarray,anyelement[,int])	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 one-dimensional)	array_position(ARRAY['sun','mon','tue','wed','thu','fri','sat'], 'mon')	2
array_positions(anyarray,anyelement)	int[]	returns an array of subscripts of all occurrences of the second argument in the array given as first argument (array must be one-dimensional)	array_positions(ARRAY['A','A','B','A'], 'A')	{1,2,4}
array_prepend(anyelement,anyarray)	anyarray	append an element to the beginning of an array	array_prepend(1, ARRAY[2,3])	{1,2,3}
array_remove(anyarray,anyelement)	anyarray	remove all elements equal to the given value from the array (array must be one-dimensional)	array_remove(ARRAY[1,2,3,2], 2)	{1,3}
array_replace(anyarray,anyelement,anyelement)	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}
array_to_string(anyarray,text[,text])	text	concatenates array elements using supplied delimiter and optional null string	array_to_string(ARRAY[1, 2, 3, NULL, 5], ',', '*')	1,2,3,*,5
array_upper(anyarray,int)	int	returns upper bound of the requested array dimension	array_upper(ARRAY[1,8,3,7], 1)	4
cardinality(anyarray)	int	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(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])	12(2 rows)
unnest(anyarray,anyarray[, ...])	setof anyelement, anyelement [, ...]	expand multiple arrays (possibly of different types) to a set of rows. This is only allowed in the FROM clause; seeSection 7.2.1.4	unnest(ARRAY[1,2],ARRAY['foo','bar','baz'])	1 foo2 barNULL baz(3 rows)

Inarray_positionandarray_positions, each array element is compared to the searched value usingIS NOT DISTINCT FROMsemantics.

Inarray_position,NULLis returned if the value is not found.

Inarray_positions,NULLis returned only if the array isNULL; if the value is not found in the array, an empty array is returned instead.

Instring_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.

Instring_to_array, if the null-string parameter is omitted or NULL, none of the substrings of the input will be replaced by NULL. Inarray_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 ofstring_to_arrayfrom pre-9.1 versions ofPostgreSQL. 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 alsoSection 9.20about the aggregate functionarray_aggfor use with arrays.