Concatenate/merge array values during grouping/aggregation

Question

I have a table with the an array column type:

 title       tags
\"ridealong\";\"{comedy,other}\"
\"ridealong\";\"{comedy,tragedy}\"
\"freddyjason\";\"{horror         


        

Answer 1

The obvious solution would be the LATERAL join (which also suggested by @CraigRinger), but that is added to PostgreSQL in 9.3.

In 9.1 you cannot avoid the sub-query, but you can simplify it:

SELECT title, array_agg(DISTINCT tag)
FROM (SELECT title, unnest(tags) FROM my_test) AS t(title, tag)
GROUP BY title;

SQL Fiddle