postgresql 数组应用

Operator Description Example Result @H_403_5@ @H_403_5@ @H_403_5@ @H_403_5@ @H_403_5@ @H_403_5@ @H_403_5@ @H_403_5@ @H_403_5@ @H_403_5@ @H_403_5@ @H_403_5@ @H_403_5@ @H_403_5@

`=`	equal	`ARRAY[1.1,2.1,3.1]::int[] = ARRAY[1,2,3]`	`t`
`<>`	not equal	`ARRAY[1,3] <> ARRAY[1,4]`	`t`
`<`	less than	`ARRAY[1,3] < ARRAY[1,4]`	`t`
`>`	greater than	`ARRAY[1,4,3] > ARRAY[1,4]`	`t`
`<=`	less than or equal	`ARRAY[1,3] <= ARRAY[1,3]`	`t`
`>=`	greater than or equal	`ARRAY[1,3] >= ARRAY[1,3]`	`t`
`@>`	contains	`ARRAY[1,3] @> ARRAY[3,1]`	`t`
`<@`	is contained by	`ARRAY[2,7] <@ ARRAY[1,7,6]`	`t`
`&&`	overlap (have elements in common)	`ARRAY[1,3] && ARRAY[2,1]`	`t`
`\|\|`	array-to-array concatenation	`ARRAY[1,3] \|\| ARRAY[4,5,6]`	`{1,3,6}`
`\|\|`	array-to-array concatenation	`ARRAY[1,3] \|\| ARRAY[[4,6],[7,8,9]]`	`{{1,3},{4,6},{7,9}}`
`\|\|`	element-to-array concatenation	`3 \|\| ARRAY[4,6]`	`{3,6}`
`\|\|`	array-to-element concatenation	`ARRAY[4,6] \|\| 7`	`{4,6,7}`

Array Functions

Function Return Type Description Example Result @H_403_5@ @H_403_5@ @H_403_5@ @H_403_5@ @H_403_5@ @H_403_5@ @H_403_5@ @H_403_5@ @H_403_5@ @H_403_5@ @H_403_5@ @H_403_5@ @H_403_5@

`array_append(anyarray,anyelement)`	`anyarray`	append an element to the end of an array	`array_append(ARRAY[1,2],3)`	`{1,3}`
`array_cat(anyarray,anyarray)`	`anyarray`	concatenate two arrays	`array_cat(ARRAY[1,3],ARRAY[4,5])`	`{1,5}`
`array_ndims(anyarray)`	`int`	returns the number of dimensions of the array	`array_ndims(ARRAY[[1,[4,6]])`	`2`
`array_dims(anyarray)`	`text`	returns a text representation of array's dimensions	`array_dims(ARRAY[[1,6]])`	`[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}`
`array_length(anyarray,int)`	`int`	returns the length of the requested array dimension	`array_length(array[1,1)`	`3`
`array_lower(anyarray,int)`	`int`	returns lower bound of the requested array dimension	`array_lower('[0:2]={1,3}'::int[],1)`	`0`
`array_prepend(anyelement,anyarray)`	`anyarray`	append an element to the beginning of an array	`array_prepend(1,ARRAY[2,3])`	`{1,3}`
`array_to_string(anyarray,text [,text])`	`text`	concatenates array elements using supplied delimiter and optional null string	`array_to_string(ARRAY[1,NULL,5],','*')`	`1,*,5`
`array_upper(anyarray,int)`	`int`	returns upper bound of the requested array dimension	`array_upper(ARRAY[1,7],1)`	`4`
`string_to_array(text,text])`	`text[]`	splits string into array elements using supplied delimiter and optional null string	`string_to_array('xx~^~yy~^~zz','~^~','yy')`	`{xx,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[1,3]) INTERSECT SELECT
UNNEST(array[2,4]) );
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 {2,5} 中是否包含4

1> mrapp=# select array[2,5] @> 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[2,4);
array_contains_value
----------------------
t
(1 行记录)

3. 数组转字符串

postgresql 数组应用

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