有没有办法将以下结果转换为数组？
select pg_tables from pg_tables
这将只返回一列，但数据类型不是数组。
编辑：我使用的是 PostgreSql 9.1.4
更新：我需要一个相当于下面的SQL语句，不需要写列名，适用于每个表：
select
string_to_array(
schemaname || '|' ||
tablename || '|' ||
tableowner || '|' ||
coalesce(tablespace,'') || '|' ||
hasindexes || '|' ||
hasrules || '|' ||
hastriggers
,'|')
from
pg_tables
【问题讨论】：
标签： sql postgresql
可能是这样的：http://www.sqlfiddle.com/#!1/d41d8/364
select translate(string_to_array(x.*::text,',')::text,'()','')::text[]
from pg_tables as x
工作原理（由内而外），5 个步骤：
第一个：
select x.*::text from pg_tables as x;
样本输出：
| X |
----------------------------------------------------------------
| (pg_catalog,pg_statistic,postgres,,t,f,f) |
| (pg_catalog,pg_type,postgres,,t,f,f) |
第二个：
select string_to_array(x.*::text,',') from pg_tables as x;
样本输出：
| STRING_TO_ARRAY |
---------------------------------------------
| (pg_catalog,pg_statistic,postgres,,t,f,f) |
| (pg_catalog,pg_type,postgres,,t,f,f) |
第三：
select string_to_array(x.*::text,',')::text from pg_tables as x;
样本输出：
| STRING_TO_ARRAY |
-------------------------------------------------
| {(pg_catalog,pg_statistic,postgres,"",t,f,f)} |
| {(pg_catalog,pg_type,postgres,"",t,f,f)} |
第四：
select translate( string_to_array(x.*::text,',')::text, '()', '') from pg_tables as x
样本输出：
| TRANSLATE |
-----------------------------------------------
| {pg_catalog,pg_statistic,postgres,"",t,f,f} |
| {pg_catalog,pg_type,postgres,"",t,f,f} |
最后：
select translate( string_to_array(x.*::text,',')::text, '()', '')::text[]
from pg_tables as x
样本输出：
| TRANSLATE |
-------------------------------------------
| pg_catalog,pg_statistic,postgres,,t,f,f |
| pg_catalog,pg_type,postgres,,t,f,f |
现场测试：http://www.sqlfiddle.com/#!1/d41d8/373
为了证明它有效：
with a as
(
select translate( string_to_array(x.*::text,',')::text, '()', '')::text[] as colArray
from pg_tables as x
)
select row_number() over(), unnest(colArray)
from a;
样本输出：
| ROW_NUMBER | UNNEST |
----------------------------------------
| 1 | pg_catalog |
| 1 | pg_statistic |
| 1 | postgres |
| 1 | |
| 1 | t |
| 1 | f |
| 1 | f |
| 2 | pg_catalog |
| 2 | pg_type |
| 2 | postgres |
| 2 | |
| 2 | t |
| 2 | f |
| 2 | f |
【讨论】：
record_expand Postgresql Windows 的库 (pltoolbox.dll)，pgFoundry 上的那个是以 Linux 为中心的，它是编译为pltoolbox.out
另一种方法，使用hstore类型，这样更健壮，可以解决字段值中的逗号
添加hstore contrib 类型，执行一次：
CREATE EXTENSION hstore;
创建这个函数：
create or replace function hstore_to_array(r hstore) returns text[] as
$$
begin
return array(select (each(r)).value);
end;
$$ language 'plpgsql';
然后试试这个：
select hstore_to_array(hstore(r)) from pg_tables r limit 10;
输出：
hstore_to_array
---------------------------------------------------
{f,pg_statistic,t,pg_catalog,postgres,NULL,f}
{f,pg_type,t,pg_catalog,postgres,NULL,f}
{f,pg_attribute,t,pg_catalog,postgres,NULL,f}
{f,xx,t,public,postgres,NULL,f}
{f,yy,t,public,postgres,NULL,f}
{f,tblx,f,public,postgres,NULL,f}
{f,pg_authid,t,pg_catalog,postgres,pg_global,f}
{f,pg_proc,t,pg_catalog,postgres,NULL,f}
{f,pg_class,t,pg_catalog,postgres,NULL,f}
{f,pg_database,t,pg_catalog,postgres,pg_global,f}
(10 rows)
另一个例子：
create table Beatle(firstname text, middlename text, lastname text);
insert into Beatle(firstname, middlename, lastname) values
('John','Winston','Lennon'),
('Paul','','McCartney'),
('George',NULL,'Harrison'),
('Ringo','my passions are ring,drum and shades','Starr');
查询：
select hstore_to_array(hstore(b)) from Beatle b;
输出：
hstore_to_array
------------------------------------------------------
{Lennon,John,Winston}
{McCartney,Paul,""}
{Harrison,George,NULL}
{Starr,Ringo,"my passions are ring,drum and shades"}
(4 rows)
我们可以看到，即使是逗号的值也被正确地保留了。
不过，精明的读者会注意到上述输出中的某些内容。 hstore 函数不会保留字段的原始顺序。为了保留它，将表放在子查询上，即
select hstore_to_array(hstore(b)) from (select * from Beatle) as b
输出：
hstore_to_array
------------------------------------------------------
{John,Winston,Lennon}
{Paul,"",McCartney}
{George,NULL,Harrison}
{Ringo,"my passions are ring,drum and shades",Starr}
(4 rows)
使用的参考：http://okbob.blogspot.com/2009/10/dynamic-access-to-record-fields-in.html
更新
看起来通过子查询保留列排序只是侥幸。我尝试进行排序（例如在名字上）。
select hstore_to_array(hstore(b))
from (select * from Beatle order by firstname) as b
输出不再保留原始列顺序：
hstore_to_array
------------------------------------------------------
{Harrison,George,NULL}
{Lennon,John,Winston}
{McCartney,Paul,""}
{Starr,Ringo,"my passions are ring,drum and shades"}
(4 rows)
将进一步研究如何保留原始列顺序。
更新
如果您需要对表进行排序，为了保留原始列顺序，请将ORDER BY 放在子查询之外：
select hstore_to_array(hstore(b))
from (select * from Beatle) as b order by firstname;
输出：
hstore_to_array
------------------------------------------------------
{George,NULL,Harrison}
{John,Winston,Lennon}
{Paul,"",McCartney}
{Ringo,"my passions are ring,drum and shades",Starr}
(4 rows)
现在是正确的。
从内存表中选择也可以：
select hstore_to_array(hstore(b))
from
(
select * from
(values
('John',1940,'Winston','Lennon'),
('Paul',1942,'','McCartney'),
('George',1943,NULL,'Harrison'),
('Ringo',1940,'my passions are ring,drum and shades','Starr')
) as x(Firstname,BirthYear,Middlename,Lastname)
) as b
order by BirthYear desc, Firstname desc
输出：
hstore_to_array
-----------------------------------------------------------
{George,1943,NULL,Harrison}
{Paul,1942,"",McCartney}
{Ringo,1940,"my passions are ring,drum and shades",Starr}
{John,1940,Winston,Lennon}
(4 rows)
更新
原来功能hstore_to_array已经是一个内置功能，只需使用avals：http://www.postgresql.org/docs/9.1/static/hstore.html
select
avals (hstore(b))
from
(
select * from
(values
('John',1940,'Winston','Lennon'),
('Paul',1942,'','McCartney'),
('George',1943,NULL,'Harrison'),
('Ringo',1940,'my passions are ring,drum and shades','Starr')
) as x(Firstname,BirthYear,Middlename,Lastname)
) as b
order by BirthYear desc, Firstname desc;
输出：
avals
-----------------------------------------------------------
{George,1943,NULL,Harrison}
{Paul,1942,"",McCartney}
{Ringo,1940,"my passions are ring,drum and shades",Starr}
{John,1940,Winston,Lennon}
(4 rows)
另一个示例：
select avals(hstore(b))
from (select * from Beatle) as b order by Firstname;
输出：
avals
------------------------------------------------------
{George,NULL,Harrison}
{John,Winston,Lennon}
{Paul,"",McCartney}
{Ringo,"my passions are ring,drum and shades",Starr}
(4 rows)
只需使用avalsツ
现场测试：http://www.sqlfiddle.com/#!1/d41d8/388
请注意，虽然 sqlfiddle 输出没有数组指示符（大括号）和 “我的激情是戒指、鼓和阴影” 上的双引号，但 avals 结果是一个数组和其中带逗号的字符串在实际结果中有双引号，你可以在你的 pgAdmin 或 psql 上测试它
【讨论】：
此函数适用于所有极端情况，包括 NULL 值、空字符串或值中的特殊字符。
CREATE OR REPLACE FUNCTION f_rows_to_arr(_tbl text)
RETURNS SETOF text[] AS
$BODY$
BEGIN
RETURN QUERY EXECUTE '
SELECT ARRAY[' || (
SELECT string_agg(quote_ident(attname) || '::text', ',')
FROM pg_catalog.pg_attribute
WHERE attrelid = _tbl::regclass -- valid, visible table name
AND attnum > 0 -- exclude tableoid & friends
AND attisdropped = FALSE -- exclude dropped columns
) || ' ]
FROM ' || _tbl::regclass;
END;
$BODY$ LANGUAGE plpgsql;
呼叫：
SELECT * FROM f_rows_to_arr ('mytbl');
regclass 的强制转换避免了 SQLi。此版本中未对列进行排序。
this related answer中使用的技术和链接的更多解释。
【讨论】：
string_to_array 可能会有所帮助：
SELECT string_to_array(pg_tables::text,','::text) FROM pg_tables;
【讨论】：