postgresql 数组应用

qmya00

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 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_prepend(anyelement, anyarray)
anyarray
append an element to the beginning of an array
array_prepend(1, ARRAY[2,3])
{1,2,3}


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


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])

1
2

(2 rows)
　　下面列举几个可能不容易查询出来的东西：
　　1. pg中查看两个数组之间有多少个重叠的数据 并且去重的方法
　　example :
　　mrapp=# SELECT  array( select UNNEST(array[1,2,3,3])         INTERSECT   SELECT
UNNEST(array[2,3,4]) );
 array
-------
 {2,3}
(1 行记录)

2. PG中没有现成的查询一个数组是否包含一个值的方法，但可以有替代方法
　　example :  查询 数组 {2,3,4,5} 中是否包含4
　　1> mrapp=# select array[2,3,4,5] @> array[4];
 ?column?
----------
 t
(1 行记录)
　　2> 自己封装函数 通过迭代循环吧
　　mrapp=# create or replace function array_contains_value(integer[], integer) retu
rns boolean as
mrapp-# $BODY$
mrapp$# declare
mrapp$# index integer;
mrapp$# begin
mrapp$# for index in 1..array_length($1 , 1) loop
mrapp$# if $1[index] = $2 then
mrapp$# return true;
mrapp$# end if;
mrapp$# end loop;
mrapp$# return false;
mrapp$# end;
mrapp$# $BODY$
mrapp-# language plpgsql;
CREATE FUNCTION
mrapp=# select array_contains_value(array[2,3,4,5] , 4);
 array_contains_value
----------------------
 t
(1 行记录)
　　3. 数组转字符串