array_agg用于数组类型

Question

我正试图array_agg在Postgresql中使用数组类型,但我无法弄清楚这是否可行,如果可行,该怎么做.我的查询的相关部分如下所示:

array_agg(ARRAY[e.alert_type::text, e.id::text, cast(extract(epoch from e.date_happened) as text)] order by e.date_happened asc, e.id asc)

我得到的错误是 ERROR: could not find array type for data type text[]

这是可能的还是我应该尝试寻找另一种方法？

谢谢!

Answer 1

您可以编写自定义聚合来处理特定的数组数组,例如:

DROP TABLE IF EXISTS e;
CREATE TABLE e
(
    id serial PRIMARY KEY,
    alert_type text,
    date_happened timestamp with time zone
);

INSERT INTO e(alert_type, date_happened) VALUES
    ('red', '2011-05-10 10:15:06'),
    ('yellow', '2011-06-22 20:01:19');

CREATE OR REPLACE FUNCTION array_agg_custom_cut(anyarray)
RETURNS anyarray
    AS 'SELECT $1[2:array_length($1, 1)]'
LANGUAGE SQL IMMUTABLE;

DROP AGGREGATE IF EXISTS array_agg_custom(anyarray);
CREATE AGGREGATE array_agg_custom(anyarray)
(
    SFUNC = array_cat,
    STYPE = anyarray,
    FINALFUNC = array_agg_custom_cut,
    INITCOND = $${{'', '', ''}}$$
);

查询:

SELECT
    array_agg_custom(
        ARRAY[
            alert_type::text,
            id::text,
            CAST(extract(epoch FROM date_happened) AS text)
        ])
FROM e;

结果:

              array_agg_custom              
--------------------------------------------
 {{red,1,1305036906},{yellow,2,1308787279}}
(1 row)

编辑:

这是第二种,更短的方式(也就是说,你不需要array_agg_custom_cut函数,但是你ARRAY在查询中看到了额外的级别):

CREATE AGGREGATE array_agg_custom(anyarray)
(
    SFUNC = array_cat,
    STYPE = anyarray
);

SELECT
    array_agg_custom(
        ARRAY[
            ARRAY[
                alert_type::text,
                id::text,
                CAST(extract(epoch FROM date_happened) AS text)
            ]
        ])
FROM e;

结果:

              array_agg_custom              
--------------------------------------------
 {{red,1,1305036906},{yellow,2,1308787279}}
(1 row)