postgresql – 当串联两列时,如何在字符串agg中添加顺序

SELECT string_agg( distinct a || '-' || b,',' ORDER BY a,b) 
FROM table;

上面的sql给出了错误

ERROR: in an aggregate with disTINCT,ORDER BY expressions must appear in argument list

解决方法

对于 the documentation：

If disTINCT is specified in addition to an order_by_clause,then all the ORDER BY expressions must match regular arguments of the aggregate; that is,you cannot sort on an expression that is not included in the disTINCT list.

所以试试吧

select string_agg(distinct a || '-' || b,' order by a || '-' || b)
from a_table;

或在派生表中使用distinct：

select string_agg(a || '-' || b,' order by a,b)
from (
    select distinct a,b
    from a_table
    ) s;