postgresql 数组应用

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