How can I create a view with a column as a CSV of multiple other columns?

Question

I have a table with columns bar1 , bar2 , bar3 . Is there a way I can create a view with a column bar which is a CSV of bar1 , bar2 , and bar3 ?

Also, if bar2 is null or bar3 is null, then I don't want extraneous commas.

bar1 bar2 bar3   bar
---- ---- ----   ---
bat  bats bass = bat,bats,bass
bim  bis       = bim,bis

Answer 1

One way to do it with a case expression.

select trim(trailing ',' from
            case when bar1 is not null then bar1||',' end ||
            case when bar2 is not null then bar2||',' end ||
            case when bar3 is not null then bar3 end) bar
from t

Sample Demo

Answer 2

Some databases support a function called concat_ws() that does exactly this.

In Oracle, it is easy enough for three columns:

select trim(both ',' from replace(bar1 || ',' || bar2 || ',' || bar3, ',,', ',')) as bar
from . . .