sql - PostgreSQL 交叉表/数据透视表问题

Question

我有一个prefs 表，下面是相关的列:

mydb=> SELECT pref_id, pref_name, pref_value FROM prefs;
 pref_id |  pref_name   |   pref_value
---------+--------------+----------------
       1 | PagerNumber  | 2125551234
       2 | PagerCarrier | @att.com
       3 | PagerCarrier | @something.com

我想制作这样的东西:

 section |  pager_number  | pager_carrier
---------+----------------+---------------
       1 | 2125551234     |
       2 |                | @att.com
       3 |                | @something.com

所以我使用了交叉表，按照 stackoverflow 上的这个例子:PostgreSQL Crosstab Query

SELECT row_name AS section,
       category_1::text AS pager_number,
       category_2::text AS pager_carrier
FROM crosstab('select pref_id::bigint, pref_name::text, pref_value::text
    FROM prefs')
AS ct (row_name bigint, category_1 text, category_2 text);

所有值都进入 pager_number，pager_carrier 留空:

 section |  pager_number  | pager_carrier
---------+----------------+---------------
       1 | 2125551234     |
       2 | @att.com       |
       3 | @something.com |

谁能看到发生了什么？

Answer 1

测试用例(提供示例数据的首选方式):

CREATE TEMP TABLE prefs (pref_id int, pref_name text, pref_value text);

INSERT INTO prefs VALUES 
 (1, 'PagerNumber' , '2125551234')
,(2, 'PagerCarrier', '@att.com')
,(3, 'PagerCarrier', '@something.com');

查询:

SELECT *
FROM   crosstab(
       'SELECT pref_id, pref_name, pref_value
        FROM   prefs
        ORDER  BY 1, 2',

       $$VALUES ('PagerNumber'::text), ('PagerCarrier')$$
       )
AS x (section text, pager_number bigint, pager_carrier text);

准确返回问题中描述的结果。如果 PagerNumber 不是有效的 bigint 数字，请改用 text。

您在问题中提到的答案已经过时，而且从一开始就不正确。我添加了一个 proper answer with explanation and links over there.