postgresql string_agg 没有与给定名称匹配的函数
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string_agg No function matches the given name
提问by Sarit
I have relational database and would like to use string_agg()since it seems fit to my need.
I want :
我有关系数据库并且想使用string_agg()它，因为它似乎适合我的需要。
我想要 ：
product_id | quiz_id
-----------+----------
1 | 1,6
2 | 2,7
3 | 3,8
4 | 4
Here is my database.
这是我的数据库。
select quiz_id , product_id, lastmodified from dugong.quiz;
quiz_id | product_id | lastmodified
---------+------------+-------------------------------
1 | 1 | 2015-11-11 14:46:55.619162+07
2 | 2 | 2015-11-11 14:46:55.619162+07
3 | 3 | 2015-11-11 14:46:55.619162+07
4 | 4 | 2015-11-11 14:46:55.619162+07
5 | 5 | 2015-11-11 14:46:55.619162+07
6 | 1 | 2015-11-11 14:46:55.619162+07
7 | 2 | 2015-11-11 14:46:55.619162+07
8 | 3 | 2015-11-11 14:46:55.619162+07
My attempt :
Refer to document.
How to concatenate strings of a string field in a PostgreSQL 'group by' query?http://www.postgresql.org/docs/current/static/sql-expressions.html#SYNTAX-AGGREGATES
我的尝试：
参考文档。
如何在 PostgreSQL 'group by' 查询中连接字符串字段的字符串？http://www.postgresql.org/docs/current/static/sql-expressions.html#SYNTAX-AGGREGATES
select product_id , string_agg(quiz_id, ',' order by lastmodified) from dugong.quiz;
ERROR: function string_agg(integer, unknown) does not exist
LINE 1: select product_id , string_agg(quiz_id, ',' order by lastmod...
^
HINT: No function matches the given name and argument types. You might need to add explicit type casts.
Postgres version :
PostgresApp 9.4.4.1
Postgres 版本：
PostgresApp 9.4.4.1
Update :
@code-monk
It still error.
更新：
@code-monk 它仍然出错。
select product_id , string_agg(quiz_id::int, ',' order by lastmodified) from dugong.quiz;
ERROR: function string_agg(integer, unknown) does not exist
LINE 1: select product_id , string_agg(quiz_id::int, ',' order by la...
^
HINT: No function matches the given name and argument types. You might need to add explicit type casts.
Question :
What is wrong with my query?
问题：
我的查询有什么问题？
回答by Abhishek
Try this:
尝试这个：
select product_id , string_agg(quiz_id::character varying, ',' order by lastmodified)
from quiz group by product_id;
String_aggfunction works with String values only ,You are getting the error because quiz_idis integer.
String_agg函数仅适用于字符串值，您收到错误，因为它quiz_id是整数。
I have converted it to character varyingand added group by for grouping the data product ID wise.
我已将其转换为character varying并添加了 group by 以明智地对数据产品 ID 进行分组。
SQL Fiddle Example:http://sqlfiddle.com/#!15/9dafe/1
SQL 小提琴示例：http://sqlfiddle.com/#!15/9dafe/1
