How to add order by in string agg, when two columns are concatenated.

Question

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

The above sql giving error

SQL

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

How to resolve the issue.

What I have tried:

I have tried with above sql which mentioned in above problem window.

Posted 10-Nov-16 18:36pm

Member 10256268

Updated 10-Nov-16 20:02pm

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jgakenhe · Answer 1 · 2016-11-10T20:02:00

With this kind of error, I typically use a subquery to do my dirty work. After playing around with this for a few minutes on SQL Fiddle[^][^], I came up with the SQL script below.

SQL

CREATE TABLE item
(
itemid integer,
item character varying(50)
);

INSERT INTO item(itemid, item)VALUES (1, 'pizza');
INSERT INTO item(itemid, item)VALUES (2, 'cake');
INSERT INTO item(itemid, item)VALUES (3, 'sandwich');


select string_agg(itemid || '-' || item,' | ') FROM ((SELECT DISTINCT item, itemid FROM item ORDER BY itemid)) t;