PostgreSQL数组使用

原文：https://my.oschina.net/Kenyon/blog/133974

1.数组的定义 
 不一样的维度元素长度定义在数据库中的实际存储都是一样的，数组元素的长度和类型必须要保持一致，并且以中括号来表示。 
合理的： 
array[1,2]            --一维数组 
array[[1,2],[3,5]]  --二维数组 
'{99,889}' 

不合理的: 
array[[1,2],[3]]                     --元素长度不一致 
array[[1,2],['Kenyon','good']]  --类型不匹配

[postgres@localhost ~]$ psql
psql (9.2.4)
Type "help" for help.
postgres=# create table t_kenyon(id serial primary key,items int[]);
NOTICE:  CREATE TABLE will create implicit sequence "t_kenyon_id_seq" for serial column "t_kenyon.id"
NOTICE:  CREATE TABLE / PRIMARY KEY will create implicit index "t_kenyon_pkey" for table "t_kenyon"
CREATE TABLE
postgres=# d+ t_kenyon
                                              Table "public.t_kenyon"
Column |   Type    |                       Modifiers                       | Storage  | Stats target | Description
--------+-----------+-------------------------------------------------------+----------+--------------+-------------
id     | integer   | not null default nextval('t_kenyon_id_seq'::regclass) | plain    |              |
items  | integer[] |                                                       | extended |              |
Indexes:
    "t_kenyon_pkey" PRIMARY KEY, btree (id)
Has OIDs: no

postgres=# create table t_ken(id serial primary key,items int[4]);
NOTICE:  CREATE TABLE will create implicit sequence "t_ken_id_seq" for serial column "t_ken.id"
NOTICE:  CREATE TABLE / PRIMARY KEY will create implicit index "t_ken_pkey" for table "t_ken"
CREATE TABLE

postgres=# d+ t_ken
                                              Table "public.t_ken"
 Column |   Type    |                     Modifiers                      | Storage  | Stats target | Description 
--------+-----------+----------------------------------------------------+----------+--------------+-------------
 id     | integer   | not null default nextval('t_ken_id_seq'::regclass) | plain    |              | 
 items  | integer[] |                                                    | extended |              | 
Indexes:
    "t_ken_pkey" PRIMARY KEY, btree (id)
Has OIDs: no

数组的存储方式是extended的。

2.数组操作

a.数据插入（两种方式）

postgres=# insert into t_kenyon(items) values('{1,2}');
INSERT 0 1
postgres=# insert into t_kenyon(items) values('{3,4,5}');
INSERT 0 1
postgres=# insert into t_kenyon(items) values(array[6,7,8,9]);
INSERT 0 1
postgres=# select * from t_kenyon;
id |   items  
----+-----------
  1 | {1,2}
  2 | {3,4,5}
  3 | {6,7,8,9}
(3 rows)

b.数据删除

postgres=# delete from t_kenyon where id = 3;
DELETE 1
postgres=# delete from t_kenyon where items[1] = 4;
DELETE 0
postgres=# delete from t_kenyon where items[1] = 3;
DELETE 1

c.数据更新

往后追加
postgres=# update t_kenyon set items = items||7;
UPDATE 1
postgres=# select * from t_kenyon;
id |  items 
----+---------
  1 | {1,2,7}
(1 row)

postgres=# update t_kenyon set items = items||'{99,66}';
UPDATE 1
postgres=# select * from t_kenyon;
id |      items      
----+------------------
  1 | {1,2,7,55,99,66}
(1 row)

往前插
postgres=# update t_kenyon set items = array_prepend(55,items) ;
UPDATE 1
postgres=# select * from t_kenyon;
id |        items       
----+---------------------
  1 | {55,1,2,7,55,99,66}
(1 row)

d.数据查询

postgres=# insert into t_kenyon(items) values('{3,4,5}');
INSERT 0 1

postgres=# select * from t_kenyon where id = 1;
id |        items       
----+---------------------
  1 | {55,1,2,7,55,99,66}
(1 row)

postgres=# select * from t_kenyon where items[1] = 55;
id |        items       
----+---------------------
  1 | {55,1,2,7,55,99,66}
(1 row)

postgres=# select * from t_kenyon where items[3] = 5;
id |  items 
----+---------
  4 | {3,4,5}
(1 row)

postgres=# select items[1],items[3],items[4] from t_kenyon;
items | items | items
-------+-------+-------
    55 |     2 |     7
     3 |     5 |     
(2 rows)

postgres=# select unnest(items) from t_kenyon where id = 4;
unnest
--------
      3
      4
      5
(3 rows)

e.数组比较

postgres=# select ARRAY[1,2,3] <= ARRAY[1,2,3];
?column?
----------
t
(1 row)

f.数组字段类型转换

postgres=# select array[['11','12'],['23','34']]::int[];
       array      
-------------------
{{11,12},{23,34}}
(1 row)

postgres=# select array[[11,12],[23,34]]::text[];
       array      
-------------------
{{11,12},{23,34}}
(1 row)

3.数组索引

postgres=# create table t_kenyon(id int,items int[]);
CREATE TABLE
postgres=# insert into t_kenyon values(1,'{1,2,3}');
INSERT 0 1
postgres=# insert into t_kenyon values(1,'{2,4}');
INSERT 0 1
postgres=# insert into t_kenyon values(1,'{34,7,8}');
INSERT 0 1
postgres=# insert into t_kenyon values(1,'{99,12}');
INSERT 0 1
postgres=# create index idx_t_kenyon on t_kenyon using gin(items);
CREATE INDEX
postgres=# set enable_seqscan = off;
postgres=# explain select * from t_kenyon where items@>array[2];
                                QUERY PLAN                                 
---------------------------------------------------------------------------
 Bitmap Heap Scan on t_kenyon  (cost=8.00..12.01 rows=1 width=36)
   Recheck Cond: (items @> '{2}'::integer[])
   ->  Bitmap Index Scan on idx_t_kenyon  (cost=0.00..8.00 rows=1 width=0)
         Index Cond: (items @> '{2}'::integer[])
(4 rows)

1.数组的定义 
 不一样的维度元素长度定义在数据库中的实际存储都是一样的，数组元素的长度和类型必须要保持一致，并且以中括号来表示。 
合理的： 
array[1,2]            --一维数组 
array[[1,2],[3,5]]  --二维数组 
'{99,889}' 

不合理的: 
array[[1,2],[3]]                     --元素长度不一致 
 array[[1,2],['Kenyon','good']]  --类型不匹配

[postgres@localhost ~]$ psql
psql (9.2.4)
Type "help" for help.
postgres=# create table t_kenyon(id serial primary key,items int[]);
NOTICE:  CREATE TABLE will create implicit sequence "t_kenyon_id_seq" for serial column "t_kenyon.id"
NOTICE:  CREATE TABLE / PRIMARY KEY will create implicit index "t_kenyon_pkey" for table "t_kenyon"
CREATE TABLE
postgres=# d+ t_kenyon
                                              Table "public.t_kenyon"
Column |   Type    |                       Modifiers                       | Storage  | Stats target | Description
--------+-----------+-------------------------------------------------------+----------+--------------+-------------
id     | integer   | not null default nextval('t_kenyon_id_seq'::regclass) | plain    |              |
items  | integer[] |                                                       | extended |              |
Indexes:
    "t_kenyon_pkey" PRIMARY KEY, btree (id)
Has OIDs: no

postgres=# create table t_ken(id serial primary key,items int[4]);
NOTICE:  CREATE TABLE will create implicit sequence "t_ken_id_seq" for serial column "t_ken.id"
NOTICE:  CREATE TABLE / PRIMARY KEY will create implicit index "t_ken_pkey" for table "t_ken"
CREATE TABLE

postgres=# d+ t_ken
                                              Table "public.t_ken"
 Column |   Type    |                     Modifiers                      | Storage  | Stats target | Description 
--------+-----------+----------------------------------------------------+----------+--------------+-------------
 id     | integer   | not null default nextval('t_ken_id_seq'::regclass) | plain    |              | 
 items  | integer[] |                                                    | extended |              | 
Indexes:
    "t_ken_pkey" PRIMARY KEY, btree (id)
Has OIDs: no

数组的存储方式是extended的。