在 Postgresql 中的字符串中排序逗号分隔值答案

【问题标题】：order comma separated values in a string in Postgresql在 Postgresql 中的字符串中排序逗号分隔值
【发布时间】：2021-01-08 23:56:50
【问题描述】：

有什么办法可以按升序或降序重新排列字符串的值？

即值：u,a,c,a 到 a,a,c,u

【问题讨论】：

为什么要在一个字段中存储多个值？这是解决问题的秘诀

标签： string postgresql sql-order-by postgresql-9.1 greenplum

【解决方案1】：

你可以通过在你的字符串上做一个 unnest 来打破多行中的值，然后对其进行分组

按 ASC 顺序获取结果

WITH cte AS (
        SELECT id, unnest(string_to_array(str, ',')) as str
        FROM test_string
        order by 1,2 
     )
select ID, string_agg(str,',') final_string  
from cte 
group by id
order by final_string ;

按 DESC 顺序获取结果

WITH cte AS (
        SELECT id, unnest(string_to_array(str, ',')) as str
        FROM test_string
        order by 1,2 desc
     )
select ID, string_agg(str,',') final_string  
from cte 
group by id
order by final_string desc;

您可以使用以下代码重现该场景。

    drop table if exists test_string;
create table test_string (id integer, str varchar(100));

insert into test_string (id, str) values (1, 'q,w,r');
insert into test_string (id, str) values (2, 'a,e,c');
insert into test_string (id, str) values (3, 'a,z,e');       
        
-- Getting results in ASC order
WITH cte AS (
        SELECT id, unnest(string_to_array(str, ',')) as str
        FROM test_string
        order by 1,2 
     )
select ID, string_agg(str,',') final_string  
from cte 
group by id
order by final_string ;

-- Getting results in DESC order
WITH cte AS (
        SELECT id, unnest(string_to_array(str, ',')) as str
        FROM test_string
        order by 1,2 desc
     )
select ID, string_agg(str,',') final_string  
from cte 
group by id
order by final_string desc;

【讨论】：