Question

can I know how do i merge arrays according to an identifier:

    Column1    Column2
--------------------------
    1          {"a","b"}
    1          {"c"}
    2          {"d"}
    2          {"w"}

output:

    Column1    Column2
--------------------------
    1          {"a","b","c"}
    2          {"d","w"}

Have tried array_agg but that is not the appropriate function for merging the array. using version 8.4 at the moment.

Answer 1

CREATE AGGREGATE array_concat(TEXT[]) (
    SFUNC = array_cat,
    STYPE = TEXT[],
    INITCOND = '{}'
);

And assuming your table is “a” and the columns affected are “n” and “t”:

 SELECT array_concat(t) FROM a GROUP BY n;