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 [, ...]
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.
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