数组

在 PostgreSQL 中,你可以创建任何内置,用户定义或枚举类型的数组。默认情况下,Array 没有限制,但你可以指定它。

声明一个数组

SELECT integer[];
SELECT integer[3];
SELECT integer[][];
SELECT integer[3][3];
SELECT integer ARRAY;
SELECT integer ARRAY[3];

创建一个数组

SELECT '{0,1,2}';
SELECT '{{0,1},{1,2}}';
SELECT ARRAY[0,1,2];
SELECT ARRAY[ARRAY[0,1],ARRAY[1,2]];

访问阵列

默认情况下,PostgreSQL 对数组使用一种基于编号的约定,即 n 个元素的数组以 array[1] 开头,以 array[n] 结尾。

--accesing a spefific element
WITH arr AS (SELECT ARRAY[0,1,2] int_arr) SELECT int_arr[1] FROM arr;

int_arr        0
(1 row)

--sclicing an array
WITH arr AS (SELECT ARRAY[0,1,2] int_arr) SELECT int_arr[1:2] FROM arr;

int_arr    {0,1}
(1 row)

获取有关阵列的信息

--array dimensions (as text)
with arr as (select ARRAY[0,1,2] int_arr) select array_dims(int_arr) from arr;

array_dims       [1:3]
(1 row)

--length of an array dimension
 WITH arr AS (SELECT ARRAY[0,1,2] int_arr) SELECT array_length(int_arr,1) FROM arr;

 array_length
 --------------
              3
 (1 row)

--total number of elements across all dimensions
 WITH arr AS (SELECT ARRAY[0,1,2] int_arr) SELECT cardinality(int_arr) FROM arr;
 
 cardinality
 -------------
             3
 (1 row)

数组函数

将被添加