Aggregate string values to a list

问题

I am trying to work some very simple logic to transform an unpivoted column into what essentially amounts to a grouped list. However, having troubles doing this efficiently.

Essentially, I have a data set that looks as follows:

CUST_ID     ORDER
1           Cake
1           Bread
2           Cake
3           Cake
3           Bread
3           Croissant
4           Croissant

But would like to output it as follows:

CUST_ID     ORDERS
1           Cake
1           Bread, Cake
3           Cake, Bread, Croissant
4           Croissant

I have tried subqueries (which I cannot get to work), but this seems brutal nonetheless:

SELECT CUST_ID, SELECT (ORDER FROM table GROUP BY CUST_ID)
FROM table
GROUP BY CUSTT_ID

Any ideas?

回答1:

Based on this SO question, Redshift now has a LISTAGG() analytic function which you can use.

SELECT CUST_ID,
       LISTAGG("ORDER", ', ')
WITHIN GROUP (ORDER BY "ORDER")
OVER (PARTITION BY CUST_ID) AS CUST_ID
FROM Table
ORDER BY CUST_ID

来源：https://stackoverflow.com/questions/43931929/aggregate-string-values-to-a-list